U.S. patent application number 16/470201 was filed with the patent office on 2020-01-16 for filter medium, method for manufacturing same, and filter unit comprising same.
The applicant listed for this patent is AMOGREENTECH CO., LTD.. Invention is credited to Ui Young JEONG, In Yong SEO.
Application Number | 20200016545 16/470201 |
Document ID | / |
Family ID | 62558962 |
Filed Date | 2020-01-16 |
United States Patent
Application |
20200016545 |
Kind Code |
A1 |
SEO; In Yong ; et
al. |
January 16, 2020 |
FILTER MEDIUM, METHOD FOR MANUFACTURING SAME, AND FILTER UNIT
COMPRISING SAME
Abstract
A filter medium according to one embodiment of the present
invention comprises: a first support having a plurality of pores; a
nanofiber web comprising nanofibers disposed on upper and lower
portions of the first support and forming a three-dimensional
network structure, and a hydrophilic coating layer formed on at
least a part of an outer surface of the nanofibers, wherein the
hydrophilic coating layer is formed of a hydrophilic coating
composition comprising a hydrophilic polymer compound having at
least one functional group selected from a hydroxyl group and a
carboxyl group and a crosslinking agent comprising at least one
sulfone group; and a second support having a plurality of pores
interposed between the first support and the nanofiber web.
Inventors: |
SEO; In Yong; (Seoul,
KR) ; JEONG; Ui Young; (Incheon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AMOGREENTECH CO., LTD. |
Gimpo-si, Gyeonggi-do |
|
KR |
|
|
Family ID: |
62558962 |
Appl. No.: |
16/470201 |
Filed: |
December 14, 2017 |
PCT Filed: |
December 14, 2017 |
PCT NO: |
PCT/KR2017/014676 |
371 Date: |
June 14, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 2325/02 20130101;
B32B 2262/12 20130101; B32B 5/26 20130101; B32B 37/02 20130101;
B32B 2255/02 20130101; B01D 65/08 20130101; B32B 2305/20 20130101;
B32B 2323/04 20130101; B32B 2329/04 20130101; B32B 2262/0253
20130101; B32B 2262/0238 20130101; B01D 2323/30 20130101; B32B
2327/12 20130101; B01D 2325/36 20130101; C02F 1/44 20130101; B01D
39/20 20130101; B32B 2255/26 20130101; B01D 71/32 20130101; B01D
65/02 20130101; B32B 2307/726 20130101; B32B 5/022 20130101; B01D
69/02 20130101; B01D 67/0002 20130101; B01D 67/002 20130101; B32B
37/24 20130101; B01D 69/06 20130101; B01D 39/16 20130101; B01D
67/0093 20130101; B32B 37/182 20130101; B01D 2321/04 20130101; B01D
63/08 20130101; B01D 67/0088 20130101; B01D 2323/39 20130101; B32B
2307/728 20130101; B32B 2323/10 20130101; B01D 2323/02 20130101;
B32B 2037/243 20130101; C02F 1/442 20130101 |
International
Class: |
B01D 65/08 20060101
B01D065/08; B01D 63/08 20060101 B01D063/08; B01D 65/02 20060101
B01D065/02; B01D 69/06 20060101 B01D069/06; B01D 67/00 20060101
B01D067/00; C02F 1/44 20060101 C02F001/44; B01D 69/02 20060101
B01D069/02; B32B 5/02 20060101 B32B005/02; B32B 5/26 20060101
B32B005/26; B32B 37/18 20060101 B32B037/18; B32B 37/02 20060101
B32B037/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 15, 2016 |
KR |
10-2016-0171438 |
Dec 15, 2016 |
KR |
10-2016-0171448 |
Dec 15, 2016 |
KR |
10-2016-0171451 |
Dec 15, 2016 |
KR |
10-2016-0171452 |
Claims
1. A filter medium comprising: a first support having a plurality
of pores; nanofiber webs disposed above and below the first support
and comprising nanofibers forming a three-dimensional network
structure and a hydrophilic coating layer formed on at least a part
of an outer surface of the nanofibers and formed of a hydrophilic
coating composition including a hydrophilic polymer compound
including one or more types of functional groups selected from a
hydroxyl group and a carboxyl group and a crosslinking agent
including one or more sulfonic groups; and a second support
interposed between the first support and the nanofiber webs and
having a plurality of pores.
2. The filter medium of claim 1, wherein the hydrophilic polymer
compound is polyvinyl alcohol having a degree of polymerization of
500 to 2,000 and a degree of saponification of 85 to 90%.
3. The filter medium of claim 1, wherein the crosslinking agent
comprises sulfosuccinic acid and poly(styrene sulfonic acid-maleic
acid) at a weight ratio of 1:3 to 1:10.
4. The filter medium of claim 1, wherein the hydrophilic coating
layer is formed by crosslinking the hydrophilic polymer compound
using the crosslinking agent.
5. The filter medium of claim 1, wherein the hydrophilic coating
composition comprises 80 to 150 parts by weight of the crosslinking
agent with respect to 100 parts by weight of the hydrophilic
polymer compound.
6. The filter medium of claim 1, wherein the hydrophilic coating
composition comprises 1,000 to 20,000 parts by weight of a
wettability enhancer with respect to 100 parts by weight of the
hydrophilic polymer compound.
7. The filter medium of claim 6, wherein the wettability enhancer
is isopropyl alcohol.
8. The filter medium of claim 1, wherein the hydrophilic coating
layer has a thickness of 5 to 20% in comparison to an average
diameter of the nanofibers.
9. The filter medium of claim 1, wherein the nanofiber web has an
average pore diameter of 0.1 to 3 .mu.m and a porosity of 40 to
90%.
10. The filter medium of claim 1, wherein the nanofibers have an
average diameter of 50 to 450 nm.
11. The filter medium of claim 1, wherein the first support and the
second support are any one of a non-woven fabric, a woven fabric,
and a knitted fabric.
12. The filter medium of claim 1, wherein the first support
comprises a first composite fiber which comprises a support
component and a low melting point component and is disposed to
expose at least a part of the low melting point component on an
outer surface, and the first support and the second support are
bonded through fusion between the low melting point component of
the first composite fiber and a low melting point component of a
second composite fiber.
13. The filter medium of claim 1, wherein the first support has a
thickness of 90% or more of a thickness of an entirety of the
filter medium and has a basis weight of 250 to 800 g/m.sup.2.
14. The filter medium of claim 1, wherein the second support
comprises a second composite fiber which comprises a support
component and a low melting point component and is disposed to
expose at least a part of the low melting point component on an
outer surface, and the low melting point component of the second
composite fiber is fused onto the nanofiber web.
15. The filter medium of claim 1, wherein the second support has a
basis weight of 35 to 80 g/m.sup.2 and a thickness of 150 to 250
.mu.m.
16. A method of manufacturing a filter medium, comprising: (1)
forming a fiber web using nanofibers formed by electrospinning a
spinning solution; (2) manufacturing lamination by laminating the
fiber web with a second support; (3) forming a hydrophilic coating
layer using a hydrophilic coating composition including a
hydrophilic polymer compound including one or more types of
functional groups selected from a hydroxyl group and a carboxyl
group on at least a part of an outer surface of the nanofibers of
the fiber web included in the lamination and a crosslinking agent
including at least one sulfonic group; and (4) disposing and
laminating the lamination including the hydrophilic coating layer
on each of both sides of a first support such that the second
support comes into contact with the first support.
17. The method of claim 16, wherein the operation (3) comprises:
(3-1) forming the hydrophilic coating layer on the lamination by
treating the hydrophilic coating composition; and (3-2) removing
the hydrophilic coating layer formed on the second support by
cleaning the lamination on which the hydrophilic coating layer is
formed.
18. A flat filter unit comprising: the filter medium according to
claim 1; and a support frame including a flow path, through which a
filtrate filtered by the filter medium is discharged to the
outside, and supporting an edge of the filter medium.
Description
TECHNICAL FIELD
[0001] The present invention relates to a filter medium, and more
particularly, to a filter medium, a method of manufacturing the
same, and a filter unit including the same.
BACKGROUND ART
[0002] Separation membranes may be classified, according to pore
sizes thereof, into a microfilter (MF) membrane, an ultrafiltration
(UF) membrane, a nanofiltration (NF) membrane, and a reverse
osmosis (RO) membrane.
[0003] Although the above separation membranes have differences in
a purpose and a pore size thereof, they are filter media formed of
fiber, porous polymer filter media, or have the form of a composite
membrane in common.
[0004] Meanwhile, some of a variety of foreign substances included
in water to be treated may remain in pores of a filter medium on
which water treatment is repetitively performed, or an attached
layer may be formed on a surface of the filter medium. Here, there
is a problem in which foreign substances which remain in the filter
medium degrade filtration performance. To solve this, it is common
to remove foreign substances which remain in the filter medium by
applying a high pressure to the filter medium in a direction
opposite to a path through which the water to be treated flows in,
is filtered by, and flows out from the filter medium. However, the
high pressure applied while the filter medium is cleaned may cause
damage of the filter medium, and a problem of delamination may
occur in the case of a filter medium having a multilayer
structure.
[0005] Generally, since most filter medium materials capable of
being manufactured by electrospinning are hydrophobic, filter media
manufactured using the same have excellent performance in chemical
resistance, strength, and the like but have disadvantages such as
low filtration performance and severe contamination. To overcome
such disadvantages, enhancing hydrophilicity of a filter medium
manufactured using a hydrophobic polymer has been attempted using a
variety of methods.
[0006] Representatively, there is a method of adsorbing
water-soluble polymer materials onto a surface of a filter medium.
In this case, there is a problem in which when a water-soluble
polymer comes into contact with water, the polymer is easily
detached from the hydrophobic filter medium such that
hydrophilicity thereof is divested. Also, since a hydrophilic
polymer is generally modified into the form of a film only on a
surface layer of the filter medium, a grafting percent is low.
[0007] Also, there is a method of mixing and emitting fiber forming
components for manufacturing a filter medium with hydrophilic
polymer materials. In this case, it is very difficult to adjust
solubility and a residual state of the hydrophilic polymer
materials such that filtration properties change or the hydrophilic
polymer materials are gradually eluted as time passes.
[0008] Accordingly, it is urgent to develop a filter medium capable
of minimizing deformation and damage to a shape and a structure of
the medium in a backwashing process performed at high pressure
simultaneously while easily securing a flow path so as to have a
high flow rate and a quick water-treatment speed, to easily control
contamination through a balance between hydrophilicity and
hydrophobicity, to have excellent filtration performance with
respect to contaminants having positive ions such as a cationic
compound and the like, and to improve water permeability and
chemical resistance.
DISCLOSURE
Technical Problem
[0009] The present invention is directed to providing a filter
medium which is uniformly coated with hydrophilic components such
that water permeability and chemical resistance are improved,
contaminants are easily controlled, filtration performance with
respect to contaminants having positive ions such as a cationic
compound and the like is excellent, and a method of manufacturing
the same.
[0010] The present invention is also directed to providing a filter
medium having excellent antibacterial and disinfection properties
and a method of manufacturing the same.
[0011] The present invention is also directed to providing a filter
medium which is uniformly coated with a cationic coating layer so
as to have improved filtration performance with respect to
contaminants having negative ions such as microbes, an anionic
compound, viruses, and the like, and a method of manufacturing the
same.
[0012] The present invention is directed to provide a filter medium
in which nanoparticles are uniformly dispersed in fiber such that
an interface capable of coming into direct contact with
contaminants is formed to have an excellent antibacterial effect,
and a method of manufacturing the same.
[0013] The present invention is also directed to providing a filter
medium in which deformation and damage to a shape and a structure
of the filter medium in a water treatment operation is minimized
simultaneously while a flow path is easily secured so as to have a
high flow rate and a quick treatment speed, and a method of
manufacturing the same.
[0014] The present invention is also directed to providing a filter
medium in which a flow path can be secured at high pressure
applied, and delamination, damage to a membrane, and the like can
be minimized, and durability is high in a backwashing process, and
a method of manufacturing the same.
[0015] The present invention is also directed to providing a flat
filter unit and a filter module which are variously applicable to a
water treatment field using a filter medium having excellent water
permeability and durability.
Technical Solution
[0016] A first embodiment of the present invention is directed to
provide a filter medium including a first support having a
plurality of pores, nanofiber webs disposed above and below the
first support and including nanofibers forming a three-dimensional
network structure and a hydrophilic coating layer formed on at
least a part of an outer surface of the nanofibers and formed of a
hydrophilic coating composition including a hydrophilic polymer
compound including one or more types of functional groups selected
from a hydroxyl group and a carboxyl group and a crosslinking agent
including one or more sulfonic groups, and second supports
interposed between the first support and the nanofiber webs and
having a plurality of pores.
[0017] The hydrophilic polymer compound may be polyvinyl alcohol
having a degree of polymerization in a range of 500 to 2,000 and a
degree of saponification in a range of 85 to 90%.
[0018] The crosslinking agent may include sulfosuccinic acid and
poly(styrene sulfonic acid-maleic acid) at a weight ratio of 1:3 to
1:10.
[0019] The hydrophilic coating layer may be formed by crosslinking
the hydrophilic polymer compound using the crosslinking agent.
[0020] The hydrophilic coating composition may include 80 to 150
parts by weight of the crosslinking agent with respect to 100 parts
by weight of the hydrophilic polymer compound.
[0021] The hydrophilic coating composition may include 1,000 to
20,000 parts by weight of a wettability enhancer with respect to
100 parts by weight of the hydrophilic polymer compound.
[0022] The wettability enhancer may be isopropyl alcohol.
[0023] The hydrophilic coating layer may have a thickness of 5 to
20% in comparison to an average diameter of the nanofibers.
[0024] The nanofiber web may have an average pore diameter of 0.1
to 3 .mu.m and a porosity of 40 to 90%.
[0025] The nanofibers may have an average diameter of 50 to 450
nm.
[0026] The first support and the second supports may be any one of
a non-woven fabric, a woven fabric, and a knitted fabric.
[0027] The first support may include a first composite fiber which
includes a support component and a low melting point component and
is disposed to expose at least a part of the low melting point
component on an outer surface, and the first support and the second
supports may be bonded through fusion between the low melting point
component of the first composite fiber and a low melting point
component of a second composite fiber.
[0028] The first support may have a thickness of 90% or more of a
thickness of an entirety of the filter medium and may have a basis
weight of 250 to 800 g/m.sup.2
[0029] The second support may include a second composite fiber
which includes a support component and a low melting point
component and is disposed to expose at least a part of the low
melting point component on an outer surface, and the low melting
point component of the second composite fiber may be fused onto the
nanofiber web.
[0030] The second support may have a basis weight of 35 to 80
g/m.sup.2 and a thickness of 150 to 250 .mu.m.
[0031] Another aspect of the present invention provides a method of
manufacturing a filter medium. The method includes (1) forming a
fiber web using nanofibers formed by electrospinning a spinning
solution, (2) manufacturing lamination by laminating the fiber web
with a second support, (3) forming a hydrophilic coating layer
using a hydrophilic coating composition including a hydrophilic
polymer compound including one or more types of functional groups
selected from a hydroxyl group and a carboxyl group on at least a
part of an outer surface of the nanofibers of the fiber web
included in the lamination and a crosslinking agent including at
least one sulfonic group, and (4) disposing and laminating the
lamination including the hydrophilic coating layer on each of both
sides of a first support such that the second support comes into
contact with the first support.
[0032] The operation (3) may include (3-1) forming the hydrophilic
coating layer on the lamination by treating the hydrophilic coating
composition and (3-2) removing the hydrophilic coating layer formed
on the second support by cleaning the lamination on which the
hydrophilic coating layer is formed.
[0033] A second embodiment of the present invention provides a
filter medium including a first support having a plurality of
pores, nanofiber webs disposed above and below the first support
and including nanofibers forming a three-dimensional network
structure and a silver antibacterial layer formed on at least a
part of an outer surface of the nanofibers, and second supports
interposed between the first support and the nanofiber webs and
having a plurality of pores.
[0034] The silver antibacterial layer may be formed through vapor
deposition to cover a part of the outer surface of the nanofibers
or formed through plating to cover an entirety of the outer
surface.
[0035] The silver antibacterial layer may have an average thickness
of 5 to 120 nm. A weight of the silver antibacterial layer may be
30 to 500% in comparison to a weight of the entirety of the
nanofibers.
[0036] The nanofiber web may have an average pore diameter of 0.1
to 3 .mu.m and a porosity of 50 to 90%.
[0037] The present invention provides a method of manufacturing a
filter medium. The method includes (1) forming a fiber web using
nanofibers formed by electrospinning a spinning solution, (2)
manufacturing a nanofiber web by providing a silver antibacterial
layer on at least a part of an outer surface of the nanofibers, (3)
laminating the nanofiber web with a second support, and (4)
laminating the nanofiber web and the second support, which are
laminated, on each of both sides of a first support such that the
second support comes into contact with the first support.
[0038] The operation (2) may be performed using an electroless
plating method.
[0039] The method may further include, before the operation (2), an
operation of pretreating a surface of the nanofibers to improve
adhesion of silver with respect to the nanofibers.
[0040] The pretreatment operation may be a catalyst-treatment
operation or a nanofiber etching operation.
[0041] The operation (2) may be any one selected from the group
consisting of sputtering, ion plating, arc deposition, ion beam
assisted deposition, and resistance heating vacuum evaporation.
[0042] The method may further include, before the operation (2),
cleaning the nanofiber web and forming a nonvolatile primer layer
having polarity on a surface of the cleaned nanofiber web.
[0043] A third embodiment of the present invention provides a
filter medium including a first support having a plurality of
pores, nanofiber webs disposed above and below the first support
and including nanofibers forming a three-dimensional network
structure and a positively charged coating layer formed on at least
a part of an outer surface of the nanofibers, and second supports
interposed between the first support and the nanofiber webs and
having a plurality of pores.
[0044] The positively charged coating layer may include one or more
types of metal complexing compounds selected from the group
consisting of silver, copper, zinc, cadmium, mercury, antimony,
gold, platinum, palladium, and a mixture thereof.
[0045] The positively charged coating layer may include one or more
types of compounds selected from the group consisting of aluminate,
aluminum alkoxide, cationic silica, polyethyleneimine,
melamine-formaldehyde, polyamine-epichlorohydrin, and aliphatic
polyamine.
[0046] The aluminate may include one or more types of compounds
selected from the group consisting of aluminum sulfate, sodium
aluminate, aluminum chloride, aluminum nitrate, and aluminum
hydroxide. The aluminum alkoxide may include one or more types of
compounds selected from the group consisting of aluminum
isopropoxide, aluminum ethoxide, and aluminum t-butoxide.
[0047] The positively charged coating layer may have a thickness of
5 to 20% in comparison to an average diameter of the
nanofibers.
[0048] The positively charged coating layer may be formed by curing
a coating composition including a solvent, a positively charged
compound, and a binder, and the positively charged coating layer
may include the positively charged compound and the cured binder at
a weight ratio of 1:0.03 to 1:1.7.
[0049] The filter medium may further include a hydrophilic coating
layer interposed between the positively charged coating layer and
the outer surface of the nanofibers and having a thickness of 5 to
20% of an average diameter of the nanofibers.
[0050] The positively charged coating layer may be formed by
vapor-depositing the positively charged compound on a part of the
outer surface of the nanofibers or formed by plating an entirety of
the outer surface with the positively charged compound.
[0051] Yet another aspect of the present invention provides a
method of manufacturing a filter medium. The method includes (1)
forming a fiber web using nanofibers formed by electrospinning a
spinning solution, (2) manufacturing a nanofiber web by providing a
positively charged coating layer including a positively charged
compound on at least a part of an outer surface of the nanofibers,
(3) laminating the nanofiber web with a second support, and (4)
laminating the nanofiber web and the second support, which are
laminated, on each of both sides of a first support such that the
second support comes into contact with the first support.
[0052] The operation (2) may include (2-1) preparing a positively
charged coating composition including a solvent, a positively
charged compound, and a binder and (2-2) manufacturing the
nanofiber web including the positively charged coating layer by
treating the fiber web with the positively charged coating
composition.
[0053] The method may further include forming a hydrophilic coating
layer between the operations (1) and (2).
[0054] In the operation (2), the positively charged coating layer
may be formed by performing any one selected from the group
consisting of sputtering, ion plating, arc deposition, ion beam
assisted deposition, and resistance heating vacuum evaporation on
the positively charged compound.
[0055] A fourth embodiment of the present invention provides a
filter medium including nanofiber webs having a three-dimensional
network structure having a plurality of pores and formed by
laminating nanofibers including silver nanoparticles, and porous
second supports interposed between the first support and the
nanofiber webs.
[0056] An average particle size of the silver nanoparticles may be
10 to 500 nm.
[0057] A weight of the silver nanoparticles may be 1 to 3% of an
overall weight.
[0058] Even another aspect of the present invention provides a
method of manufacturing a filter medium. The method includes (1)
laminating a nanofiber web including silver nanofibers with a
second support and (2) disposing and laminating the nanofiber web
and the second support, which are laminated, on each of both sides
of a first support such that the second support comes into contact
with the first support. Here, a thickness of the first support is
90% or more of a thickness of an entirety of the filter medium.
[0059] The operation (1) may include (1-1) forming the nanofiber
web by electrospinning a spinning solution, in which silver salts
dissolve, on the second support and (1-2) laminating the nanofiber
web with the second support by applying heat and pressure to both
sides of the second support on which the nanofiber web is
formed.
[0060] The silver salts may be one of silver nitrate, silver
sulfate, and silver chloride.
[0061] A further aspect of the present invention provides a flat
filter unit including the above-described filter medium according
to the present invention and a support frame including a flow path,
through which a filtrate filtered by the filter medium is
discharged to the outside, and supporting an edge of the filter
medium.
Advantageous Effects
[0062] According to the present invention, in a filter medium,
deformation and damage to a shape and a structure of the filter
medium may be minimized and a flow path may be easily secured so as
to have a high flow rate in a water treatment operation. Also,
despite high pressure applied in backwashing, an extended use
period is provided due to excellent durability of the filter
medium, excellent water permeability and chemical resistance are
provided by uniformly coating a surface thereof with hydrophilic
components, contamination is easily controlled, and filtration
performance with respect to contaminants having positive ions such
as a cationic compound and the like is excellent such that the
filter medium is variously applicable to a variety of water
treatment fields. Also, a nanofiber web includes silver such that
an excellent antibacterial effect capable of disinfecting a variety
of bacteria included in water to be treated may be provided. Also,
due to excellent electrochemical adsorption performance, excellent
filtration efficiency with respect to contaminants such as
microbes, cationic compounds, viruses, and the like may be
provided.
DESCRIPTION OF DRAWINGS
[0063] FIG. 1 is a cross-sectional view of a filter medium
according to one embodiment of the present invention;
[0064] FIGS. 2A and 2B are schematic diagrams illustrating
adsorption with respect to contaminants such as a cationic compound
and the like;
[0065] FIGS. 3A and 3B are schematic diagrams illustrating
adsorption with respect to contaminants such as an anionic
compound, viruses, and the like;
[0066] FIG. 4 is a schematic diagram illustrating lamination of the
filter medium according to one embodiment of the present invention
in which FIG. 4A is a view illustrating lamination between a
nanofiber web and a second support, and FIG. 4B is a view
illustrating lamination performed by arranging the laminated
nanofiber web and second structure on both sides of a first
support;
[0067] FIG. 5 is a view illustrating a flat filter unit according
to one embodiment of the present invention in which FIG. 5A is a
perspective view of the filter unit, and FIG. 5B is a schematic
diagram illustrating a filtration flow on the basis of a
cross-sectional view taken along a line X-X' of FIG. 5A; and
[0068] FIG. 6 is a scanning electron microscope (SEM) image
illustrating a surface of the nanofiber web according to one
embodiment of the present invention.
BEST MODES
[0069] Hereinafter, embodiments of the present invention will be
described in detail with reference to the attached drawings to
allow one of ordinary skill in the art to easily carry out the
present invention. The present invention may be embodied in a
variety of different shapes and is not limited to the embodiments
disclosed herein. In order to clearly describe the present
invention, parts irrelevant to the present invention are omitted,
and the same or similar components are referred to as equal
reference numerals.
[0070] A filter medium 1000 according to a first embodiment of the
present invention includes, as shown in FIG. 1, a first support 130
including a plurality of pores, nanofiber webs 111 and 112 disposed
above and below the first support 130, and nanofibers forming a
three-dimensional network structure and a hydrophilic coating layer
formed using a hydrophilic coating composition including a
hydrophilic polymer compound including one or more functional
groups selected from a hydroxyl group and a carboxyl group and a
crosslinking agent including at least one sulfonic group on at
least a part of an outer surface of the nanofibers, and second
supports 121 and 122 including a plurality of pores and interposed
between the first support 130 and the nanofiber webs 111 and 112,
respectively.
[0071] In general, a filter medium formed only of nanofibers having
hydrophobicity has excellent chemical resistance. However, the
filter medium is applied to a water treatment filter field, and due
to the hydrophobicity of the filter medium, water affinity is
decreased such that water permeability is degraded. Here, although
water permeability of the hydrophobic filter medium may be improved
using adequate pressure, since necessary pressure is very high (150
to 300 psi), the filter medium may be damaged. Also, the filter
medium is vulnerable to contaminants having hydrophobicity and
contaminants having positive ions such that a study for treatment
of providing a filter medium with hydrophilicity and negative ions
is required.
[0072] Thus, the present invention may solve the above-described
problems by embodying the nanofiber webs 111 and 112 including the
hydrophilic coating layer formed on at least the part of the outer
surface of the nanofibers.
[0073] That is, referring to FIGS. 1, 2A, and 2B, the filter medium
1000 according to the present invention includes the second
supports 121 and 122 and the nanofiber webs 111 and 112
sequentially laminated above and below the first support 130 and
has a filtration flow in which a filtrate filtered by the nanofiber
webs 111 and 112 flows toward the first support 130. Here,
contaminants such as a cationic compound and the like, which pass
through the nanofiber webs 111 and 112, may be effectively filtered
out as shown in FIGS. 2A and 2B.
[0074] In more detail, general micro-contaminants having positive
ions may be electrochemically adsorbed with negative charges of the
hydrophilic coating layer on a surface of a plurality of nanofibers
forming the nanofiber webs due to electrostatic attraction. That
is, the hydrophilic coating layer may be formed as a polymer in
which negatively charged atoms included therein are straightly
chained or branched such that contaminants having positive ions,
which are included in a solution to be filtered, may be adsorbed
onto the hydrophilic coating layer due to electrostatic attraction
and be induced to be precipitated on the surface of the nanofiber
web to be filtered out. Here, removal performance with respect to
contaminants having positive ions may vary according to charge
density of negative charges, and the charge density may be
adequately selected in consideration of a type and charge density
of target contaminants.
[0075] The hydrophilic coating layer is formed using a hydrophilic
coating composition including a hydrophilic polymer compound
including one or more types of functional groups selected from a
hydroxyl group and a carboxyl group and a crosslinking agent
including at least one sulfonic group.
[0076] As the hydrophilic polymer compound, any hydrophilic polymer
compounds including one or more types of functional groups selected
from a hydroxyl group and a carboxyl group, which are
conventionally usable, may be used without limitation, and more
preferably, may be one of polyvinyl alcohol (PVA), ethylene vinyl
alcohol (EVOH), sodium alginate, and the like, and a mixture
thereof. As an example, PVA may be used.
[0077] When the hydrophilic polymer compound is PVA, the PVA may
have a degree of polymerization of 500 to 2000, and more
preferably, 1500 to 2000 and a degree of saponification of 85 to
90%, and more preferably, 86 to 89%. As an example, the PVA may
have a degree of polymerization of 1800 and a degree of
saponification of 88%. When the degree of polymerization of the PVA
is less than 500, the hydrophilic coating layer may not be easily
formed or may be easily taken off even when being formed. Also, a
hydrophilic degree may not be improved to a target level. When the
degree of polymerization exceeds 2000, the hydrophilic coating
layer may be excessively formed. Accordingly, a pore structure of a
fiber web layer may be changed or pores are blocked such that
porosity and a pore diameter may be degraded. Also, when the degree
of saponification of the PVA is less than 85%, forming of the
hydrophilic coating layer may be unstable and a degree of
improvement of hydrophilicity may be insignificant. When the degree
of saponification exceeds 90%, due to a strong hydrogen bond
between PVA molecules, the PVA may not be easily dissolved in a
solvent at high temperature. Even when the PVA is dissolved,
complete dissolution is difficult such that it may be difficult to
prepare a solution for forming the hydrophilic coating layer.
Accordingly, the hydrophilic coating layer may not be adequately
formed. Even when being formed, the hydrophilic coating layer may
be non-uniformly formed and some pores may be blocked such that
objective effects may not be provided.
[0078] As the crosslinking agent, any generally usable crosslinking
agents including at least one sulfonic group may be used without
limitation, and preferably, one or more types selected from the
group consisting of sulfosuccinic acid and poly(styrene sulfonic
acid-maleic acid) may be used. As an example, the crosslinking
agent may include both sulfosuccinic acid and poly(styrene sulfonic
acid-maleic acid).
[0079] The hydrophilic coating layer is formed by being crosslinked
with the hydrophilic polymer composition using the crosslinking
agent such that hydrophilicity of the filter medium is improved
simultaneously while the hydrophilic coating layer is negatively
charged such that filtration efficiency with respect to cationic
contaminants may be improved.
[0080] When the crosslinking agent includes both sulfosuccinic acid
and poly(styrene sulfonic acid-maleic acid), the crosslinking agent
may include sulfosuccinic acid and poly(styrene sulfonic
acid-maleic acid) at a weight ratio in a range of 1:3 to 1:10, and
preferably, at a weight ratio in a range of 1:5 to 1:8. As an
example, the weight ratio between sulfosuccinic acid and
poly(styrene sulfonic acid-maleic acid) may be 1:6.7. When the
weight ratio between sulfosuccinic acid and poly(styrene sulfonic
acid-maleic acid) is less than 1:3, a rate of being crosslinked
with PVA is lacking such as to degrade forming of the hydrophilic
coating layer. When the weight ratio between sulfosuccinic acid and
poly(styrene sulfonic acid-maleic acid) exceeds 1:10, a crosslinked
bond and water permeability may be degraded due to an
autoagglutination phenomenon.
[0081] Also, 80 to 150 parts by weight, and preferably, 90 to 140
parts by weight of the crosslinking agent may be included with
respect to 100 parts by weight of the hydrophilic polymer compound.
As an example, 115 parts by weight of the crosslinking agent may be
included with respect to 100 parts by weight of the hydrophilic
polymer compound. When the crosslinking agent is less than 80 parts
by weight with respect to 100 parts by weight of the hydrophilic
polymer compound, formability of the hydrophilic coating layer may
be degraded and chemical resistance and mechanical strength may be
degraded. When 150 parts by weight is exceeded, the crosslinking
agent may clump in a hydrophilic coating composition such that it
is difficult for a crosslinking reaction to be uniformly performed.
Accordingly, the coating layer may be non-uniformly formed or pores
may be reduced due to the coating layer such that a flow rate may
be decreased.
[0082] Meanwhile, due to strong hydrophobicity of nanofibers
forming a manufactured fiber web layer, even when the
above-described hydrophilic coating composition is treated, the
coating composition may not penetrate into the fiber web layer such
that it is difficult for the hydrophilic coating composition to
reach the nanofibers in the fiber web layer which flow along a
surface. Also, although the hydrophilic coating composition reaches
the inside, the hydrophilic coating layer may not be adequately
formed on an outer surface of the nanofibers. Accordingly, the
hydrophilic coating composition may further include a wettability
enhancer such that penetrability of the hydrophilic coating
composition into the fiber web layer is improved, the penetrating
hydrophilic coating composition well permeates the outer surface of
the nanofibers, and the hydrophilic coating composition is quickly
dried to coat the nanofibers before flowing down.
[0083] As the wettability enhancer, any one of components which can
improve wettability of the outer surface of the hydrophobic
nanofibers with respect to a hydrophilic solution and are easily
vaporizable and soluble in the hydrophilic coating composition may
be used without limitation. As an example, the wettability enhancer
may be one or more types of components selected from the group
consisting of isopropyl alcohol, ethyl alcohol, and methyl alcohol,
and preferably, isopropyl alcohol may be used to prevent a fiber
web from contracting due to vaporization of the wettability
enhancer and prevent a change in a pore structure of the initially
designed fiber web which is caused by the contraction. Also, 1,000
to 20,000 parts by weight, and preferably, 5,000 to 15,000 parts by
weight of the wettability enhancer may be included with respect to
100 parts by weight of polyvinyl alcohol included in the
hydrophilic coating composition. As an example, 5,000 parts by
weight of the wettability enhancer may be included with respect to
100 parts by weight of polyvinyl alcohol. When the wettability
enhancer is provided at less than 1,000 parts by weight,
improvement in wettability of the nanofibers is insignificant such
that the hydrophilic coating layer may not be easily formed and the
hydrophilic coating layer may be frequently delaminated. Also, when
the wettability enhancer is provided at more than 20,000 parts by
weight, improvement in the wettability may be insignificant and
concentrations of polyvinyl alcohol and the crosslinking agent
included in the hydrophilic coating composition are decreased such
that the hydrophilic coating layer may not be easily formed.
[0084] Meanwhile, when the nanofibers are coated with the
hydrophilic coating layer of a certain thickness or more, since an
average pore diameter and/or porosity of the nanofiber webs may
decrease due to the coated nanofibers, water permeability and
filtration efficiency may be degraded. When being coated less than
the certain thickness, since the filtration efficiency may be
significantly degraded, the hydrophilic coating layer may be formed
within a thickness range. Accordingly, the hydrophilic coating
layer according to the present invention may be formed to have a
thickness of 5 to 20%, and preferably, 8 to 18% in comparison with
an average diameter of the nanofibers. As an example, the
hydrophilic coating layer may be formed to have a thickness of 12%
in comparison with the average diameter of the nanofibers. When the
hydrophilic coating layer is formed to have a thickness of less
than 5% in comparison with the average diameter of the nanofibers,
since the hydrophilic coating layer is delaminated during a
backwashing process in which an excessive pressure is applied,
filtration efficiency may not be provided at a target level. When
the hydrophilic coating layer is formed to have a thickness of more
than 20%, it is not easy to decrease a weight of the filter medium.
Also, as a size and porosity of pores are reduced, water
permeability of the solution to be filtered may be degraded.
[0085] Next, the nanofibers forming the nanofiber webs 111 and 112
may be formed of a well-known fiber-forming component. However,
preferably, a fluorine-based compound may be included as the
fiber-forming component to provide excellent chemical resistance
and heat resistance. Through this, even through the filtrate is a
strong acid/strong alkali solution or a high-temperature solution,
filtration efficiency/flow rate at a target level and a long use
period may be provided without change in properties of the filter
medium. The fluorine-based compound may be any one of well-known
fluorine-based compounds which may manufactured using nanofibers
without limitation, and for example, may include one or more
compounds selected from the group consisting of
polytetrafluoroethylene (PTFE), a
tetrafluoroethylene-perfluoroalkyl vinyl ether (PFA) copolymer, a
tetrafluoroethylene-hexafluoropropylene (FEP) copolymer, a
tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether
(EPE) copolymer, a tetrafluoroethylene-ethylene (ETFE) copolymer,
polychlorotrifluoroethylene (PCTFE), a
chlorotrifluoroethylene-ethylene (ECTFE) copolymer, and
poly(vinylidene fluoride) (PVDF). More preferably, due to a low
manufacturing cost, nanofibers being easy to mass produce through
electrospinning, and excellent mechanical strength and chemical
resistance, the fluorine-based compound may be PVDF. Here, when the
nanofibers include PVDF as a fiber-forming component, a weight
average molecular weight of the PVDF may be 10,000 to 1,000,000,
and preferably, 300,000 to 600,000, but the PVDF is not limited
thereto.
[0086] Also, an average diameter of the nanofibers may be 50 to 450
nm, and preferably, 100 to 400 nm. As an example, the average
diameter of the nanofibers may be 250 .mu.m. A thickness of the
nanofiber webs 111 and 112 may be 0.5 to 200 .mu.m, and for
example, may be 20 .mu.m. A basis weight thereof may be 0.05 to 20
g/m.sup.2, and for example, may be 10 g/m.sup.2 but may be changed
adequately in consideration of target water permeability and
filtration efficiency and is not particularly limited in the
present invention.
[0087] Also, an average pore diameter of the nanofiber webs 111 and
112 may be 0.1 to 3 .mu.m, and preferably, 0.15 to 2 .mu.m, and for
example, may be 0.25 .mu.m. When the average pore diameter of the
nanofiber webs 111 and 112 is less than 0.1 .mu.m, water
permeability with respect to a solution to be filtered may be
degraded. When the average diameter exceeds 3 .mu.m, filtration
efficiency may not be high with respect to contaminants.
[0088] Also, porosity of the nanofiber webs 111 and 112 may be 40
to 90%, and preferably, 45 to 80%. For example, the porosity of the
nanofiber webs 111 and 112 may be 45%. When the porosity of the
nanofiber webs 111 and 112 is less than 40%, water permeability
with respect to a solution to be filtered may be degraded. When the
porosity exceeds 90%, filtration efficiency of the filter medium
with respect to contaminants may not be high.
[0089] Also, one or more layers of the nanofiber webs 111 and 112
may be included in the filter medium 1000. Here, porosity, an pore
diameter, a basis weight, a thickness, and/or the like of each
nanofiber web may be different.
[0090] Hereinafter, other components included in the filter medium
1000 will be described in detail.
[0091] First, the first support 130 supports the filter medium 1000
and forms a large flow path to more smoothly perform a filtration
process or a backwashing process. In detail, when a pressure
difference (gradient) is formed such that an internal pressure of
the filter medium is lower than an external pressure thereof during
the filtration process, the filter medium may be compressed. In
this case, a flow path through which the filtrate may flow in the
filter medium may be significantly reduced or blocked such that a
higher differential pressure is applied to the filter medium
simultaneously while a flow rate may be significantly degraded.
Also, an external force for expansion may be applied from the
inside of the filter medium toward the outside in both directions
during the backwashing process. When a mechanical strength is low,
the filter medium may be damaged by the applied external force.
[0092] The first support 130 may be provided to prevent the above
problems which occur during the filtration process and/or the
backwashing process, may be used in a water treatment field, and
may be a well-known porous member which secures mechanical
strength. For example, the first support may be non-woven fabric,
fabric, or knitted fabric.
[0093] The woven fabric refers to fabric including fibers which
have lengthwise and crosswise grain. A specific structure may be
plain weaves, twilled weaves, and the like, and densities of weft
and warp are not particularly limited. Also, the knitted fabric may
be a well-known knitted fabric, may be a weft-knitted fabric, a
warp-knitted fabric, and the like, and for example, may be tricot
in which threads are weft-knitted. Also, as shown in FIG. 1, the
first support 130 may be non-woven fabric in which fabric does not
have lengthwise and crosswise grain, and dry non-woven fabric such
as chemical-bonded non-woven fabric, thermal-bonded non-woven
fabric, aerated non-woven fabric, and the like, wet non-woven
fabric, spanless non-woven fabric, well-known non-woven fabric
manufactured using a variety of methods such as a needle-punched
fabric and a melt-blown fabric may be used.
[0094] The first support 130 may occupy 90% or more of an entirety
of a thickness of the filter medium to provide adequate mechanical
strength and to prevent durability from being degraded according to
backwashing. As an example, a thickness of the first support 130
may be 2 to 8 mm, preferably, 2 to 5 mm, and more preferably, 3 to
5 mm. For example, the first support 130 may have a thickness of 5
mm. When the thickness is less than 2 mm, adequate mechanical
strength which can bear frequent backwashing may not be provided.
Also, in the case of a thickness of more than 8 mm, when the filter
medium is provided as a filter unit, which will be described below,
and then a plurality of such filter units are provided as a filter
module having a limited space, a degree of integration of the
filter medium per unit volume of the module may be reduced.
[0095] Preferably, the first support 130 may satisfy conditions of
the thickness simultaneously while a basis weight thereof may be
250 to 800 g/m.sup.2, and more preferably, 350 to 600 g/m.sup.2.
For example, the first support 130 may have a basis weight of 500
g/m.sup.2. When the basis weight is less than 250 g/m.sup.2, it may
be difficult to provide adequate mechanical strength and an
adhesive force with the second support may be reduced. When the
basis weight exceeds 800 g/m.sup.2, an adequate flow path may not
be formed, a flow rate may be reduced, and it may be difficult to
smoothly perform backwashing due to an increase in a differential
pressure.
[0096] Also, when the first support 130 is formed as fibers such as
non-woven fabric, an average diameter of the fibers may be 5 to 50
.mu.m, and preferably, 20 to 50 .mu.m. For example, the average
diameter of the fibers may be 35 .mu.m. Also, the average pore
diameter of the first support 130 may be 20 to 200 .mu.m, and
preferably, 30 to 180 .mu.m. As an example, the average pore
diameter of the first support 130 may be 100 .mu.m. Porosity
thereof may be 50 to 90%, and preferably, 55 to 85%. For example,
the first support 130 may have a porosity of 70% but is not limited
thereto. Any porosities and pore diameters capable of providing a
target degree of mechanical strength simultaneously while easily
forming a flow path even at high pressure by supporting the
above-described nanofiber webs 111 and 112 during the filtration
process and/or the backwashing process are available.
[0097] There is no limitation in a material of the first support
130 when the material is used as a support of a separation
membrane. As a non-limiting example thereof, a synthetic polymer
component selected from the group consisting of a polyester-based
component, a polyurethane-based component, a polyolefin-based
component, and a polyamide-based component or a natural polymer
component including cellulose may be used. However, when the first
support tends to be brittle, it may be difficult to provide a
target degree of an adhesive force in a process of laminating the
first support with the second support. This is because the first
support does not have a smooth surface like a film and may have an
uneven surface having porosity. The surface formed by fibers such
as non-woven fabric may have an unsmooth surface according to an
arrangement of fibers, deniers of fibers, and the like, and a
degree thereof may be different for each position. When a part,
which is not pressed against an interface between two laminated
layers, is present and other parts are joined, delamination between
layers may be started due to the part which is not pressed against
the interface. To solve this, it is necessary to perform a
lamination process while pressure is applied to the two layers from
both directions such that an adhesion degree of the two layers is
increased. However, in the case of a support having high
brittleness, even when a pressure is applied, there is a limit in
increasing adhesion between two layers. Since the support may be
damaged when a higher pressure is applied, a material having high
flexibility and a high elongation rate may be suitable as a
material of the first support. Preferably, the first support 130
may have a polyolefin-based material to have excellent adhesion
with the second supports 121 and 122.
[0098] Meanwhile, the first support 130 may include a low melting
point component to be bound to the second supports 121 and 122
together without an additional adhesive or adhesive layer. When the
first support 130 is whole cloth such as non-woven fabric, the
first support may be manufactured using a first composite fiber
130a including a low melting point component. The first composite
fiber 130a may include a support component and a low melting point
component and may be disposed such that at least a part of the low
melting point component is exposed from an outer surface. As an
example, the first composite fiber 130a may be a sheath-core type
composite fiber, in which the support component forms a core
portion and the low melting point component surrounds the core
portion, or a side-by-side composite fiber in which the low melting
point component is disposed on one side of the support component.
As described above, in terms of aspects of flexibility and an
elongation rate of the support, the low melting point component and
the support component may be a polyolefin. For example, the support
component may be polypropylene and the low melting point component
may be polyethylene-based component. Here, a melting point of the
low melting point component may be 60 to 180.degree. C.
[0099] Next, the second supports 121 and 122, which are disposed on
both sides of the first support 130 and the nanofiber webs 111 and
112, which are described above.
[0100] The second supports 121 and 122 support the above-described
nanofiber webs 111 and 112 and increase adhesive forces of layers
provided in the filter medium.
[0101] The second supports 121 and 122 are not particularly limited
to any components which conventionally perform a function of
supports of the filter medium and may be in the form of a woven
fabric, a knitted fabric, or non-woven fabric. The woven fabric
refers to a fabric including fibers which have lengthwise and
crosswise grain. A specific structure may be plain weaves, twilled
weaves, and the like, and densities of weft and warp are not
particularly limited. Also, the knitted fabric may be a well-known
knitted fabric and may be a weft knitted fabric, a warp knitted
fabric, and the like but is not limited particularly. Also, the
non-woven fabric means that fibers included therein have no
lengthwise and crosswise grain. Dry non-woven fabric such as
chemical-bonded non-woven fabric, thermal-bonded non-woven fabric,
aerated non-woven fabric, and the like, wet non-woven fabric,
spanless non-woven fabric, and well-known non-woven fabric
manufactured using a variety of methods such as a needle-punched
fabric and a melt-blown fabric may be used.
[0102] The second supports 121 and 122 may be, for example,
non-woven fabric. Here, fibers which form the second supports 121
and 122 may have an average diameter of 5 to 30 .mu.m. A thickness
of the second supports 121 and 122 may be 150 to 250 .mu.m, and
preferably, 160 to 240 .mu.m, and for example, may be 200
.mu.m.
[0103] Also, the second supports 121 and 122 may have an average
pore diameter of 20 to 100 .mu.m and porosity of 50 to 90%.
However, the second supports are not limited thereto, and there is
no limitation except that porosities and pore diameters capable of
providing a target degree of mechanical strength by supporting the
above-described nanofiber webs 111 and 112 and simultaneously not
impeding a flow of a filtrate which flows through the nanofiber
webs 111 and 112 should be used. As an example, the second supports
121 and 122 may have an average pore diameter of 60 .mu.m and a
porosity of 70%.
[0104] Also, a basis weight of the second supports 121 and 122 may
be 35 to 80 g/m.sup.2, more particularly, 40 to 75 g/m.sup.2, and
for example, may be 40 g/m.sup.2. When the basis weight is less
than 35 g/m.sup.2, an amount of fibers which form the second
supports and are distributed on an interface with the nanofiber
webs 111 and 112 may be small such that an effective adhesion area
of the second supports in contact with the nanofiber webs is
reduced and a target degree of an adhesive force may not be
provided. Also, problems may be present in which adequate
mechanical strength capable of supporting the nanofiber webs is not
provided and an adhesive force with the first support is reduced.
Also, when the basis weight exceeds 80 g/m.sup.2, it is difficult
to secure a target flow rate and difficult to easily perform
backwashing due to an increase in a differential pressure.
[0105] There is no limitation in a material of the second supports
121 and 122 when the material is used as a support of the filter
medium. As a non-limiting example thereof, a synthetic polymer
component selected from the group consisting of a polyester-based
component, a polyurethane-based component, a polyolefin-based
component, and polyamide-based component or a natural polymer
component including cellulose may be used.
[0106] However, the second supports 121 and 122 may be a
polyolefin-based polymer component to improve adhesion between the
above-described nanofiber webs 111 and 112 and the first support
130. Also, when the second supports 121 and 122 are whole cloth
such as non-woven fabric, the second supports 121 and 122 may be
manufactured using a second composite fiber 121a including a low
melting point component. The second composite fiber 121a may
include a support component and a low melting point component and
may be disposed such that at least a part of the low melting point
component is exposed from an outer surface. As an example, the
second composite fiber 121a may be a sheath-core type composite
fiber, in which the support component forms a core portion and the
low melting point component surrounds the core portion, or a
side-by-side composite fiber in which the low melting point
component is disposed on one side of the support component. As
described above, in terms of aspects of flexibility and an
elongation rate of the support, the low melting point component and
the support component may preferably be a polyolefin-based
component. For example, the support component may be polypropylene
and the low melting point component may be polyethylene. Here, a
melting point of the low melting point component may be 60 to
180.degree. C.
[0107] When the above-described first support 130 is provided as
the first composite fiber 130a including the low melting point
component to provide a further improved adhesive force with the
second supports 121 and 122, a more strongly fused portion arising
from fusion of the low melting point component of the first
composite fiber 130a and the low melting point components of the
second composite fiber 121a may be formed on an interface between
the first support 130 and the second support 121. Here, the first
composite fiber 130a and the second composite fiber 121a may have
the same type of material in terms of an aspect of
compatibility.
[0108] Meanwhile, an attachment process of the filter medium 1000
according to one embodiment of the present invention may be more
stably and easily performed, and a significantly high adhesive
force is provided in an interface between layers. In order to
minimize separation and delamination between layers even when a
high external force is applied due to backwashing and the like, the
first support 130 and the nanofiber webs 111 and 112 do not face
each other directly and the second supports 121 and 122 having a
smaller thickness are interposed therebetween.
[0109] Referring to FIG. 4A, since a difference between thicknesses
of the nanofiber web 2 and a second support 3, which occupies less
than 10% of an entirety of a thickness of the filter medium, is
significantly smaller than a difference between thicknesses of the
nanofiber web 2 and a first support 1, heat H1 and H2 applied from
above and below lamination of the nanofiber web 2/the second
support 3 reach an interface therebetween such that a fused portion
B is easily formed. Also, since it is easy to adjust an amount and
time of applied heat, it is advantageous for preventing
physical/chemical deformation of the nanofiber web 2. Accordingly,
when the nanofiber web 2 is bonded to the second support 3 as shown
in FIG. 4A, nanofibers may be combined with the support having an
excellent adhesive force as shown in FIG. 4B without a change in
properties of the nanofiber web 2 which is initially designed.
[0110] Meanwhile, the filter medium 1000 according to a first
embodiment of the present invention may be manufactured through
operations including (1) forming a fiber web using nanofibers
formed by electrospinning a spinning solution, (2) manufacturing
lamination by laminating the fiber web with a second support, (3)
forming a hydrophilic coating layer using a hydrophilic coating
composition including a hydrophilic polymer compound including one
or more types of functional groups selected from a hydroxyl group
and a carboxyl group on at least a part of an outer surface of the
nanofibers of the fiber web included in the lamination and a
crosslinking agent including at least one sulfonic group, and (4)
disposing and laminating the lamination including the hydrophilic
coating layer on each of both sides of a first support such that
the second support comes into contact with the first support.
[0111] First, (1) the forming of the fiber web using the nanofibers
formed by electrospinning the spinning solution will be
described.
[0112] The fiber web may be formed using any methods of forming a
three-dimensional network-shaped fiber web using nanofibers without
limitation. Preferably, the fiber web may be formed by
electrospinning a spinning solution including a fluorine-based
compound onto a second support.
[0113] The spinning solution may include, for example, a
fluorine-based compound and a solvent as the fiber-forming
component. 5 to 30 wt %, and preferably, 8 to 20 wt % of the
fluorine-based compound may be included in the spinning solution.
As an example, 15 wt % of the fluorine-based compound may be
included in the spinning solution. When the fluorine-based compound
is less than 5 wt %, it is difficult to form fibers. When being
spun, the fluorine-based compound is not spun in a fiber shape and
is sprayed in a droplet state to form a film shape. Otherwise, even
when spinning is performed, many beads are formed and the solvent
is not well volatilized such that a phenomenon in which pores are
blocked during a calendering process which will be described may
occur. Also, when the fluorine-based compound exceeds 30 wt %,
viscosity increases and solidification occurs on a surface of the
solution such that it is difficult to perform spinning for a long
time, and a diameter of fibers increases such that it is impossible
to form a fiber shape having a size of submicrometer.
[0114] As the solvent, any solvents may be used without limitation
that do not generate precipitations while dissolving the
fluorine-based compound which is a fiber-forming component and do
not influence spinning properties of nanofibers, which will be
described below. Preferably, any one or more selected from the
group consisting of r-butyrolactone, cyclohexanone, 3-hexanone,
3-heptanone, 3-octanone, N-methylpyrrolidone, dimethylacetamide,
acetone dimethyl sulfoxide, and dimethylformamide may be included.
As an example, the solvent may be a mixed solvent of
dimethylacetamide and acetone.
[0115] Nanofibers may be manufactured through a well-known
electrospinning device and method using the manufactured spinning
solution. As an example, as the electrospinning device, an
electrospinning device including a single spinning pack including
one spinning nozzle may be used or an electrospinning device
including a plurality of single spinning packs or a spinning pack
including a plurality of nozzles may be used for mass production.
Also, as an electrospinning method, dry-spinning or wet-spinning
including an external coagulating tub may be used and there is no
restriction according to the method.
[0116] When an agitated spinning solution is injected into the
electrospinning device and electrospun on a collector, for example,
on paper, a nanofiber web formed of nanofibers may be obtained. As
an example of a specific condition for the electrospinning may be
that an air pressure of air spray of an air spray nozzle provided
in a nozzle of the spinning pack may be set within a range of 0.01
to 0.2 MPa. When the air pressure is less than 0.01 MPa, there is
no effect on collection and integration. When 0.2 MPa is exceeded,
a phenomenon in which a cone of a spinning nozzle is solidified
such that a needle is blocked occurs such that difficulties may
occur in spinning. Also, when the spinning solution is spun, an
injection speed of the spinning solution per nozzle may be 10 to 30
.mu.l/min. Also, a distance between a tip of the nozzle and the
collector may be 10 to 30 cm. However, the distance is not limited
thereto and may be modified according to a purpose thereof.
[0117] Next, (2) the manufacturing of the lamination by laminating
the fiber web with the second support will be described.
[0118] When the second support is provided using low melting point
composite fibers, bonding between the fiber web and the second
support through heat fusion may be performed at the same time
through the calendering process.
[0119] Also, an additional hot-melt powder or hot-melt web may be
further interposed to bind the second support to the fiber web.
Here, a temperature of applied heat may be 60 to 190.degree. C. and
an applied pressure may be 0.1 to 10 kgf/cm.sup.2 but the
temperature and pressure are not limited thereto. However,
components such as the hot-melt powder, which is separately added
for binding, generate fumes or are melted in a process of
laminating supports or laminating a support with nanofibers and
block pores frequently such that it is impossible to achieve a flow
rate of the filter medium which is initially planned. Also, since
the components are soluble in a water treatment process such that
environmentally adverse problems may be caused, the second support
and the fiber web may be bound to each other without the
components.
[0120] Next, (3) the forming of the hydrophilic coating layer using
the hydrophilic coating composition including the hydrophilic
polymer compound including one or more types of functional groups
selected from a hydroxyl group and a carboxyl group on at least the
part of the outer surface of the nanofibers of the fiber web
included in the lamination and the crosslinking agent including at
least one sulfonic group will be described.
[0121] According to one embodiment of the present invention, the
operation (3) may include (3-1) forming the hydrophilic coating
layer on the lamination by treating the hydrophilic coating
composition and (3-2) removing the hydrophilic coating layer formed
on the second support by cleaning the lamination on which the
hydrophilic coating layer is formed.
[0122] In the operation (3-1), the hydrophilic coating composition
may include the solvent, the hydrophilic polymer compound, and the
crosslinking agent.
[0123] The solvent may include one or more types of solvents
selected from the group consisting of purified water, ethanol,
methanol, ethylene glycol, acetic acid, hexene, cyclohexene,
cyclopentane, diisobutylene, 1-pentene, carbon disulfide, carbon
tetrachloride, 1-chlorobutene, 1-chloropentane, o-xylene,
diisopropyl ether, 2-chloropropane, toluene, diethyl ether, diethyl
sulfide, dichloromethane, 4-methyl-2-propanone, tetrahydrofuran,
1,2-dichloroethane, 2-butanone, 1-nitropropane, acetone,
1,4-dioxane, ethyl acetate, methyl acetate, 1-pentanol, dimethyl
sulfoxide, aniline, nitromethane, acetonitrile, pyridine,
2-butoxyethanol, 1-propanol, and 2-propanol, but is not limited
thereto, and a well-known solvent which does not influence mixing
and properties of the hydrophilic coating composition may be
used.
[0124] Also, 0.3 to 1.5 parts by weight, and preferably, 0.5 to 1.3
parts by weight of the hydrophilic polymer compound may be included
with respect to 100 parts by weight of the solvent. As an example,
1 part by weight of the hydrophilic polymer compound may be
included with respect to 100 parts by weight of the solvent.
[0125] Meanwhile, the hydrophilic coating layer may be formed by
crosslinking the hydrophilic polymer compound using the
crosslinking agent.
[0126] The crosslinking agent may include sulfosuccinic acid and
poly(styrene sulfonic acid-maleic acid) as described above. Here,
when sulfosuccinic acid and poly(styrene sulfonic acid-maleic acid)
are added together to the solvent, cohesion may occur in the
crosslinking agent. Accordingly, as the solvent, a first solvent
and a second solvent may be used. Solutions are manufactured by
adding sulfosuccinic acid with the hydrophilic polymer compound
together to the first solvent and adding poly(styrene sulfonic
acid-maleic acid) to the second solvent, and then a first solution
manufactured using the first solvent and a second solution
manufactured using the second solvent may be mixed with each other.
Here, the first solvent and the second solvent may be the same type
of solvent or may be different solvents.
[0127] Also, the operation (3-2) is the removing of the hydrophilic
coating layer formed on the second support by cleaning the
lamination. When cleaning is performed, only the hydrophilic
coating layer formed on the second support may be removed such that
adhesion with the first support may be further improved.
[0128] Next, (4) the disposing and laminating of the lamination
including the hydrophilic coating layer on each of both sides of
the first support such that the second support comes into contact
with the first support will be described.
[0129] In the operation (4), the first support and the second
support may be melted by applying one or more of heat and pressure
and laminated in order to dispose and laminate the nanofiber web
and the second support, which are laminated, on each of both sides
of the first support. Here, a specific method of applying heat
and/or pressure may be selected from well-known methods. As a
non-limiting example, a general calendering process may be used in
which a temperature of applied heat may be 70 to 190.degree. C.
Also, when the calendering process is performed, the process may be
divided into several operations and be performed a plurality of
times. For example, secondary calendering may be performed after
primary calendering. Here, degree(s) of heat and/or pressure, which
are/is applied in the calendering processes, may be equal or
different. The bonding between the second support and the first
support through heat fusion may be performed through fusion of the
first support and the second support such that an additional
adhesive or an adhesive layer may be omitted.
[0130] Also, a filter medium 1000 according to a second embodiment
of the present invention includes, as shown in FIG. 1, a first
support 130 including a plurality of pores, nanofiber webs 111 and
112 disposed above and below the first support 130 and including
nanofibers forming a three-dimensional network structure and a
silver (Ag) antimicrobial layer formed on at least a part of an
outer surface of the nanofibers, and second supports 121 and 122
including a plurality of pores and interposed between the first
support 130 and the nanofiber webs 111 and 112, respectively.
[0131] The nanofiber webs 111 and 112 are provided on surfaces
opposite to surfaces in contact with the second supports 121 and
122 and the first support 130, respectively. The nanofiber webs 111
and 112 may be formed by randomly arranging a single nanofiber or
several threads of nanofibers.
[0132] A filter medium formed of only conventional nanofibers may
effectively remove fine dust having a certain size and contaminants
but does not have any means which sterilizes microbes such as
bacteria and the like collected with the fine dust. Hence, the
present invention provides the filter medium which includes the
nanofiber webs 111 and 112 including the silver antibacterial layer
formed on at least the part of the outer surface of the nanofibers
so as to maintain an ability of removing fine dust and contaminants
and additionally to have improved sterilizing power and
antibacterial activity with respect to harmful microbes and the
like.
[0133] The silver antibacterial layer may be formed by
vapor-depositing silver on the nanofibers or by silver-plating the
nanofibers. Here, being formed by vapor-depositing or by plating
may cause a difference in shape of the covering silver
antibacterial layer depending on a difference in manufacturing
methods which will be described below. When the silver
antibacterial layer is formed by plating, since a method and the
like of dipping the nanofiber webs into a silver-plating solution
is used, the silver antibacterial layer may be formed to cover an
entirety of the outer surface of the nanofibers included in the
nanofiber webs. Also, when the silver antibacterial layer is formed
by vapor-depositing, since silver may be vapor-deposited only on
the nanofibers exposed at a surface of an outer surface of the
nanofiber webs, the silver antibacterial layer may be embodied such
that silver covers only a part of the outer surface of the
nanofibers exposed in order to cover the part of the outer surface
of the nanofibers.
[0134] An average thickness of the silver antibacterial layer may
be 5 to 120 nm, and preferably, 10 to 100 nm to provide excellent
water permeability and antibacterial activity simultaneously and to
maintain the antibacterial activity after backwashing. As an
example, the average thickness of the silver antibacterial layer
may be 50 nm. When the thickness of the silver antibacterial layer
is less than 5 nm, since the covering silver antibacterial layer is
delaminated during a backwashing process in which an excessive
pressure is applied, a target degree of antibacterial activity may
not be provided. Also, when the thickness of the silver
antibacterial layer exceeds 120 nm, it is not easy to decrease a
weight of the filter medium. Also, as a size and porosity of pores
are reduced, water permeability of a solution to be filtered may be
degraded.
[0135] Meanwhile, the average thickness of the silver antibacterial
layer refers to an average thickness of an silver antibacterial
layer formed by coating an outer surface of nanofibers when the
silver antibacterial layer is formed by plating and refers to an
average of an silver antibacterial layer formed on a part of an
outer surface of nanofibers when the silver antibacterial layer is
formed by vapor-depositing.
[0136] Also, in order to obtain an effect in which all of
antibacterial activity, filtration efficiency, and durability are
excellent at the same time, a weight of the silver antibacterial
layer may be 30 to 500%, and preferably, 50 to 200% in comparison
with the weight of the whole nanofibers. For example, the weight of
the silver antibacterial layer may be 60% in comparison to a weight
of the whole nanofibers when the silver antibacterial layer is
formed by vapor-depositing and may be 133% in comparison with the
weight of the whole nanofibers when the silver antibacterial layer
is formed by plating. When the weight of the silver antibacterial
layer is less than 30% in comparison with the weight of the whole
nanofibers, an antibacterial effect may be degraded. When the
weight is more than 500%, it is not easy to decrease a weight of
the filter medium and a size of pores is decreased such that water
permeability with respect to the solution to be filtered may be
degraded.
[0137] Next, description on a fiber-forming component which forms
the nanofiber webs 111 and 112 and an average diameter of the
nanofibers are equal to those of the first embodiment of the
present invention and as such will be omitted.
[0138] Also, an average pore diameter of the nanofiber webs 111 and
112 may be 0.1 to 3 .mu.m, preferably, in a range of 0.15 to 2
.mu.m, and for example, may be 0.25 .mu.m. When the average
diameter of the nanofiber webs 111 and 112 is less than 0.1 .mu.m,
water permeability with respect to a solution to be filtered may be
degraded. When the average diameter exceeds 3 .mu.m, filtration
efficiency of the filter medium may not be high and an
antibacterial effect may be degraded.
[0139] Also, porosity of the nanofiber webs 111 and 112 may be 50
to 90%, and preferably, in a range of 60 to 80%. For example, the
porosity of the nanofiber webs 111 and 112 may be 70%. When the
porosity of the nanofiber webs 111 and 112 is less than 50%, water
permeability with respect to the solution to be filtered may be
degraded. When the porosity exceeds 90%, filtration efficiency of
the filter medium may not be high and an antibacterial effect may
be degraded.
[0140] Also, description on other components included in the filter
medium 1000 are equal to those of the first embodiment of the
present invention and as such will be omitted.
[0141] Meanwhile, the filter medium 1000 according to the second
embodiment of the present invention may be manufactured through
operations including (1) forming a fiber web using nanofibers
formed by electrospinning a spinning solution, (2) manufacturing a
nanofiber web by including an silver antibacterial layer on at
least a part of an outer surface of the nanofibers, (3) laminating
the nanofiber web with a second support, and (4) disposing and
laminating the nanofiber web and the second support, which are
laminated, on each of both sides of a first support such that the
second support comes into contact with the first support.
[0142] First, (1) the forming of the fiber web using nanofibers
formed by electrospinning the spinning solution will be
described.
[0143] The fiber web may be formed using any method of forming a
three-dimensional network-shaped fiber web using nanofibers without
limitation. Preferably, the fiber web may be formed by
electrospinning a spinning solution including a fluorine-based
compound onto the second support.
[0144] The spinning solution may include, for example, a
fluorine-based compound and a solvent as the fiber-forming
component. 5 to 30 wt %, and preferably, 8 to 20 wt % of the
fluorine-based compound may be included in the spinning solution.
When the fluorine-based compound is less than 5 wt %, it is
difficult to form fibers. When being spun, the fluorine-based
compound is not spun in a fiber shape and is sprayed in a droplet
state to form a film shape. Otherwise, even when spinning is
performed, many beads are formed and the solvent is not well
volatilized such that a phenomenon in which pores are blocked
during a calendering process which will be described may occur.
Also, when the fluorine-based compound exceeds 30 wt %, viscosity
increases and solidification occurs on a surface of the solution
such that it is difficult to perform spinning for a long time, and
a diameter of fibers increases such that it is impossible to form a
fiber shape having a size of submicrometer.
[0145] As the solvent, any solvents may be used without limitation
that do not generate precipitations while dissolving the
fluorine-based compound which is a fiber-forming component and do
not influence spinning properties of nanofibers, which will be
described below. Preferably, any one or more selected from the
group consisting of r-butyrolactone, cyclohexanone, 3-hexanone,
3-heptanone, 3-octanone, N-methylpyrrolidone, dimethylacetamide,
acetone dimethyl sulfoxide, and dimethylformamide may be included.
As an example, the solvent may be a mixed solvent of
dimethylacetamide and acetone.
[0146] Description on electrospinning conditions and the like are
equal to those of the above-described first embodiment and as such
will be omitted.
[0147] Meanwhile, to add hydrophilicity to the outer surface of the
nanofibers before performing the operation (2) which will be
described below, hydrophilic coating may be performed, but the
present invention is not limited thereto.
[0148] Next, (2) the manufacturing of the nanofiber web by
including the silver antibacterial layer on at least the part of
the outer surface of the nanofibers will be described.
[0149] The operation (2) may be embodied, as described above, using
a first method of forming the silver antibacterial layer to
surround an entirety of the outer surface of the nanofibers by
plating the nanofibers forming the fiber web with silver and a
second method of forming the silver antibacterial layer on at least
the part of the outer surface of the nanofibers by vapor-depositing
silver on the nanofibers exposed at one side of the fiber web.
[0150] First, the first method of forming the silver antibacterial
layer to surround the entirety of the outer surface of the
nanofibers by plating the nanofibers forming the fiber web with
silver will be described. Although one of well-known silver-plating
methods may be used in silver plating, in consideration of
properties of the nanofibers, an electroless plating method may be
used. Hereinafter, a method of plating the outer surface of the
nanofibers forming the fiber web with silver using the electroless
plating method will be described as a reference.
[0151] The electroless silver plating method uses a substitution
reaction. In general, a method of silver-plating a surface of a
target material, in which a material to be silver-plated is dipped
into a silver-plating solution including a reducible
silver-complexing material and is reduced to silver by adding a
reductant thereto, is used.
[0152] The silver-plating solution may be a mixture solution
including a reducible solution, which is substituted for silver,
and a silver-providing solution which provides silver-complexing
material. As the reducible solution, hydrazine (N.sub.2H.sub.4),
lithium borohydride, sodium borohydride, aluminum borohydride,
sodium hypophosphite (NaH.sub.2PO.sub.2), and the like, which are
inorganic reductants, and formaldehyde (HCHO), acetaldehyde
(CH.sub.3CHO), benzaldehyde (C.sub.6H.sub.5CHO), acrolein
(CH.sub.2.dbd.CHCHO), glucose, and the like, which are organic
reductants, may be used. Among these, glucose may be used. As a
reductant aqueous solution, an aqueous solution in which
concentration of a reductant is in a range of 2 to 20% (w/v) may be
used.
[0153] As the silver-providing solution which provides a
silver-complexing material, silver sulfate, silver nitrate, silver
chloride, and the like may be used. Any well-known silver-providing
solutions may be used without limitation in a range which has no
influence on properties of the nanofibers.
[0154] The surface of the nanofibers forming the nanofiber webs 111
and 112 may be plated with silver by dipping the nanofiber webs 111
and 112 into the above-described silver-plating solution. In
consideration of a thickness of covering silver and a surface area,
the nanofiber webs 111 and 112 may be dipped into the
silver-plating solution for 1 to 10 hours.
[0155] When dipping is performed for less than one hour, the
surface of the nanofibers may not be plated adequately with silver
such that antibacterial and sterilizing performance may be
degraded. Also, when dipping is performed for more than ten hours,
the surface of the nanofibers is plated excessively with silver
such that there may be a problem in decreasing a weight of the
filter medium and a size of pores decreases such that penetration
of a solution to be filtered may be degraded.
[0156] Here, in a case of using a method of applying the reductant
to the silver-plating solution, since a reduction reaction occurs
not only on the surface of the material to be silver-plated but
also in the silver-plating solution, the surface of the nanofiber
webs are soaked in the reducible solution in a small quantity
before being dipped into the silver-plating solution such that
silver is obtained by reduction only on the surface of the
nanofiber webs so as to prevent an unnecessary reduction
reaction.
[0157] Meanwhile, in the present invention, a pretreatment process
may be performed on the fiber web before the above-described
electroless silver-plating in order to prevent antibacterial
efficiency from being degraded by the plated silver antibacterial
layer being taken off due to higher water pressure than usual in
backwashing, to prevent pores of the filter medium from being
blocked and damaged by separated metal particles, and/or to further
prevent contamination of the filtrate from being induced. Here, the
pretreatment process may be a catalyst-treatment operation or a
nanofiber etching operation.
[0158] The catalyst-treatment operation is a treatment process for
improving adhesion with a metal by initiating a chemical reaction
with the metal on a surface of a fiber which is a nonconductor
during electroless silver plating and may be an operation for
forming an electroless plating film without stains on a surface of
nanofiber. The etching operation may be a process for improving
wettability of nanofibers with respect to the plating solution and
obtaining an anchor effect.
[0159] Next, the second method of forming the silver antibacterial
layer on at least the part of the outer surface of the nanofibers
by vapor-depositing silver on the nanofibers exposed at one surface
of the fiber web will be described.
[0160] A method of vapor-depositing silver may be any one selected
from the group consisting of sputtering, ion plating, arc
deposition, ion beam assisted deposition, and resistance heating
vacuum evaporation. For example, as the method of vapor-depositing
silver, a resistance heating vacuum evaporation method may be
used.
[0161] In a resistance heating vacuum evaporation system, a silver
vapor-depositing material, which is heated in a vacuum chamber and
vaporized into a gas phase, may be provided at a top of a hot plate
and a substrate holder may be disposed at a part facing the silver
vapor-depositing material at a distance.
[0162] In the present invention, the fiber web, on which the silver
vapor-depositing material will be vapor-deposited, is wound on a
first bobbin disposed outside one side of the vacuum chamber and
the fiber web passes through a bottom of the substrate holder at a
certain speed while being guided by a guide roller in the vacuum
chamber such that vapor deposition may be performed on the surface
of the fiber web according to evaporation of the silver
vapor-depositing material. Afterwards, the nanofiber webs 111 and
112, on which the silver vapor deposition layer is formed, are
withdrawn to the other side of the vacuum chamber and are wound on
a second bobbin such that silver vapor deposition may be
consecutively performed.
[0163] Meanwhile, the present invention may further include forming
a primer layer capable of maximizing adhesion between the silver
antibacterial layer and the fiber web by performing surface
treatment on the fiber web before the forming of the silver
antibacterial layer through vapor deposition to prevent
antibacterial efficiency from being degraded by the silver
antibacterial layer being removed due to excessive water pressure
which is higher than usual in backwashing, to prevent pores of the
filter medium from being blocked and damaged by removed metal
particles, and/or to further prevent contamination of the filtrate
from being induced.
[0164] The primer layer may be formed through a process in which a
nonvolatile primer material having polarity is applied and dried at
a uniform thickness, in which methyl methacrylate, polyether
modified dimethylpolysiloxane copolymer, methyl ethyl ketone, vinyl
chloride-vinyl acetate copolymer, toluene, and the like may be
used.
[0165] Also, instead of the surface treatment of the primer layer,
an operation of performing plasma-treatment using a plasma
generator installed in the vacuum chamber before vapor deposition
may be further included. When the plasma treatment is performed on
the fiber web, the surface of the fiber web is activated such that
a polar functional group (OH- and H+) with respect to a metal
material to be vapor-deposited is assigned and cleaned and fine
prominences and depressions are formed so as to increase adhesion
between the fiber web and the silver antibacterial layer. As a
reaction gas used in the plasma treatment, any one of fluorocarbon
(CF.sub.4), argon (Ar), zenon (Ze), helium (He), nitrogen
(N.sub.2), oxygen (O.sub.2), and a mixture thereof may be used.
[0166] The nanofiber webs manufactured by performing the
above-described operation (2) may include the silver antibacterial
layer formed on at least the part of the outer surface of the
nanofibers as shown in FIG. 6.
[0167] Next, (3) the laminating of the nanofiber web with the
second support will be described.
[0168] When the second support is provided using low melting point
composite fibers, bonding between the nanofiber web and the second
support through heat fusion may be performed at the same time
through the calendering process.
[0169] Also, an additional hot-melt powder or hot-melt web may be
further interposed to bind the second support to the nanofiber web.
Here, a temperature of applied heat may be 60 to 190.degree. C. and
an applied pressure may be 0.1 to 10 kgf/cm.sup.2, but the
temperature and pressure are not limited thereto. However,
components such as the hot-melt powder, which is separately added
for binding, generate fumes or are melted in a process of
laminating supports or laminating a support with nanofibers and
block pores frequently such that it is impossible to achieve a flow
rate of the filter medium which is initially designed. Also, since
the components are soluble in a water treatment process such that
environmentally adverse problems may be caused, the second support
and the nanofiber web may be bound to each other without the
components.
[0170] Next, (4) the disposing and laminating of the nanofiber webs
and the second support, which are laminated, on each of both sides
of the first support such that the second support comes into
contact with the first support will be described.
[0171] In the operation (4), the first support and the second
support may be melted by applying one or more of heat and pressure
and laminated in order to dispose and laminate the nanofiber web
and the second support, which are laminated, on each of both sides
of the first support. Here, a specific method of applying heat
and/or pressure may be selected from well-known methods. As a
non-limiting example, a general calendering process may be used in
which a temperature of applied heat may be 70 to 190.degree. C.
Also, when the calendering process is performed, the process may be
divided into several operations and be performed a plurality of
times. For example, secondary calendering may be performed after
primary calendering. Here, degree(s) of heat and/or pressure, which
are/is applied in the calendering processes, may be equal or
different. The bonding between the second support and the first
support through heat fusion may be performed through fusion of the
first support and the second support such that an additional
adhesive or an adhesive layer may be omitted.
[0172] A filter medium 1000 according to a third embodiment of the
present invention includes, as shown in FIG. 1, a first support 130
including a plurality of pores, nanofiber webs 111 and 112 disposed
above and below the first support 130 and including nanofibers
forming a three-dimensional network structure and a positively
charged coating layer formed on at least a part of an outer surface
of the nanofibers, and second supports 121 and 122 including a
plurality of pores and interposed between the first support 130 and
the nanofiber webs 111 and 112, respectively.
[0173] In general, viruses classified as pathogenic micro-organisms
and pathogenic micro-organisms classified into cryptosporidium,
giardia, and the like are discharged into environments through
excrement of human bodies and animals and are present in not only
sewage but also surface water and underground water. Viruses have a
size in a range of 0.02 to 0.09 .mu.m, and bacteria have a size in
a range of 0.4 to 14 .mu.m. Particularly, viruses have a very small
size and thus are not treated through general filtration and form
cysts with great resistance so as to stably live in water for
several months or more.
[0174] In order to remove pathogenic micro-organisms such as
viruses, high cohesion treatment or activated carbon adsorption, or
membrane filtration are provided in a water treatment process.
Particularly, much study with respect to membrane filtration has
been performed such that practical use has been gauged in high
water purification treatment process. However, due to economical
costs and technical problems, the membrane filtration is not widely
in use even until now.
[0175] Since micro fiber filters widely used for conventional water
treatment have a small filtration area and have no electrostatic
force, efficiency decreases. Membrane filters have high filtration
efficiency but have a great loss in pressure. Accordingly, it is
surely necessary to develop a filter medium which increases
filtration efficiency with respect to micro pathogens such as
viruses by adding an electrostatic force to a fiber filter having
nano-sized pores for remedying shortcomings of a microfiber filter
and a membrane filter.
[0176] The filter medium according to the present invention may
adsorb contaminants such as viruses through electrochemical
adsorbability by forming the positively charged coating layer on
the nanofibers and simultaneously easily removing the contaminants
by embodying the nanofiber webs 111 and 112 formed by randomly
arranging one thread of a nanofiber or several threads of
nanofibers as the filter medium.
[0177] That is, referring to FIGS. 1, 3A, and 3B, the filter medium
1000 according to the present invention includes the second
supports 121 and 122 and the nanofiber webs 111 and 112
sequentially laminated above and below the first support 130 and
has a filtration flow in which a filtrate filtered by the nanofiber
webs 111 and 112 flows toward the first support 130. Here, micro
pathogens such as viruses and the like, which pass through the
nanofiber webs 111 and 112, may be effectively filtered out as
shown in FIGS. 3A and 3B.
[0178] In more detail, general micro-contaminants such as viruses
having negative ions may be electrochemically adsorbed with a
positively charged coating layer formed on a surface of a plurality
of nanofibers forming the nanofiber webs due to electrostatic
attraction. That is, the positively charged coating layer may be
formed in the form of small charged molecules of a positively
charged compound included therein or a copolymer in which
positively charged atoms are straightly chained or diverged
according to or a copolymer chain length. Contaminants, which are
included in the solution to be filtered and have positive ions, are
adsorbed with the positively charged compound of the positively
charged coating layer due to electrostatic attraction and included
to be precipitated on the surface of the nanofiber webs to be
filtered. Here, removal performance with respect to contaminants
having negative ions may vary according to charge density of the
positively charged compound, and the charge density of the
positively charged compound may be adequately selected in
consideration of a type and charge density of target
contaminants.
[0179] The positively charged coating layer may include, as the
positively charged compound, one or more metallic complex compounds
selected from the group consisting of silver, copper, zinc,
cadmium, mercury, antimony, gold, aluminum, platinum, palladium,
and a mixture thereof, and more preferably, silver and/or
copper.
[0180] Also, the positively charged coating layer may include, as
the positively charged compound, one or more types of compounds
selected from the group consisting of aluminate, aluminum alkoxide,
cationic silica, polyethyleneimine, melamine-formaldehyde,
polyamine-epichlorohydrin, and aliphatic polyamine. The aluminate
may be one or more types of compounds selected from the group
consisting of aluminum sulfate, sodium aluminate, aluminum
chloride, aluminum nitrate, and aluminum hydroxide. The aluminum
alkoxide may be one or more types of compounds selected from the
group consisting of aluminum isopropoxide, aluminum ethoxide, and
aluminum t-butoxide.
[0181] When the nanofibers are coated with the positively charged
coating layer with a certain thickness or more, since an average
pore diameter and/or porosity of the nanofiber webs may decrease
due to the coated nanofibers, water permeability and filtration
efficiency may be degraded. When the nanofibers are coated less
than the certain thickness, since the filtration efficiency may be
significantly degraded, the positively charged coating layer may be
formed within a certain thickness range. Accordingly, the
positively charged coating layer according to the present invention
may be formed to have a thickness in a range of 5 to 20%, and
preferably, in a range of 8 to 18% in comparison with an average
diameter of the nanofibers. As an example, the positively charged
coating layer may be formed to have a thickness of 12% in
comparison with the average diameter of the nanofibers. When the
positively charged coating layer is formed to have a thickness of
less than 5% in comparison with the average diameter of the
nanofibers, since the positively charged coating layer is
delaminated during a backwashing process in which an excessive
pressure is applied, filtration efficiency with respect to
contaminants such as microbes, an anionic compound, viruses, and
the like may not be provided as a target level. When the positively
charged coating layer is formed to have a thickness of more than
20%, it is not easy to decrease a weight of the filter medium.
Also, as a size and porosity of pores are reduced, water
permeability of the solution to be filtered may be degraded.
[0182] Here, a reference of the average thickness of the positively
charged coating layer may vary according to a method of forming a
positively charged coating layer which will be described. As an
example, the reference refers to an average thickness of the
positively charged coating layer formed to cover the outer surface
of the nanofibers when the positively charged coating layer is
formed using a plating method or a method using a coating
composition and refers to an average thickness of the positively
coating layer formed on a part of the outer surface of the
nanofibers when the positively charged coating layer is formed
through vapor deposition.
[0183] Meanwhile, the positively charged coating layer may be
formed by curing a coating composition including a solvent, a
positively charged compound, and a binder such that the positively
charged coating layer may include the positively charged compound
and the cured binder at a weight ratio in a range of 1:0.03 to
1:1.7, and preferably, at a weight ratio in a range of 1:0.06 to
1:0.9. As an example, the weight ratio between the positively
charged compound and the cured binder may be 1:0.2. When the weight
ratio between the positively charged compound and the cured binder
is less than 1:0.03, as the positively charged coating layer is
delaminated during a backwashing process in which an excessive
pressure is applied, durability against backwashing is degraded
such that a desirable degree of filtration efficiency with respect
to contaminants such as microbes, an anionic compound, viruses, and
the like may not be provided and the positively charged compound
may remain in a filtrate. When the weight ratio exceeds 1:1.7, as
electrostatic attraction of the positively charged compound is
relatively degraded outside the positively charged coating layer, a
desirable degree of filtration efficiency with respect to
contaminants such as microbes, an anionic compound, viruses, and
the like may not be provided and a size and porosity of pores are
reduced such that water permeability of the solution to be filtered
may be degraded.
[0184] Also, the positively charged coating layer may be formed by
vapor-depositing or plating with the positively charged compound to
cover at least a part of the outer surface of the nanofibers. Here,
since the positively charged coating layer may be formed using
different methods, the positively charged coating layer, which is
formed, may have a difference in a shape thereof. When the
positively charged coating layer is formed by plating, since a
method and the like of dipping fiber webs into a positively charged
compound plating solution is used, the positively charged coating
layer may be formed to cover an entirety of the outer surface of
nanofibers included in the fiber webs. Also, when the positively
charged coating layer is formed through vapor deposition, since the
positively charged compound may be vapor-deposited only on
nanofibers exposed at the surface of the outer surface of the
nanofiber webs on the basis of an upper part, the positively
charged coating layer may be embodied as a shape in which the
positively charged compound covers only a part of the outer surface
of the exposed nanofibers to cover the part of the outer surface of
the nanofibers.
[0185] Also, the nanofiber webs provided in the filter medium
according to the present invention may further include a
hydrophilic coating layer interposed between the positively charged
coating layer and the outer surface of the nanofibers in order to
easily form the positively charged coating layer and to further
increase adhesion between the nanofibers and the positively charged
coating layer. Here, when the positively charged coating layer is
formed of the coating composition, the hydrophilic coating layer
may be applied in cases of both plating and vapor deposition.
Preferably, applying of the hydrophilic coating layer may be
advantageous to improvement in an adhesive property of the
positively charged coating layer when the positively charged
coating layer is formed of a coating composition.
[0186] The hydrophilic coating layer may be formed including a
hydrophilic polymer or may be formed by crosslinking a hydrophilic
polymer using a crosslinking agent. The hydrophilic polymer may be
any one of PVA, EVOH, sodium alginate, and the like, and a mixture
thereof and, most preferably, may be PVA. Also, as the crosslinking
agent, any well-known crosslinking agents including a functional
group capable of crosslinking through a condensation reaction and
the like with a hydroxyl group included in the hydrophilic polymer
may be used without limitation. As an example, the functional group
may be one of a hydroxyl group, a carboxyl group, and the like.
[0187] Meanwhile, the hydrophilic coating layer may be formed by
crosslinking a crosslinking agent including PVA and a carboxyl
group in order to provide a further improved adhesive property.
[0188] The crosslinking agent may be a component including a
carboxyl group to be crosslinked with the PVA and may include, for
example, one or more types of materials selected from the group
consisting of poly(acrylic acid-maleic acid), polyacrylic acid, and
poly(styrene sulfonic acid-maleic acid). Also, the crosslinking
agent may be a multifunctional crosslinking agent including three
or more carboxyl groups for the further improved adhesive property
between the nanofibers of the hydrophilic coating layer and the
positively charged coating layer. When the crosslinking agent
includes less than three carboxyl groups, it is difficult to form a
hydrophilic coating layer. Even when a hydrophilic coating layer is
formed, the hydrophilic coating layer may be easily delaminated due
to low adhesion. As an example, a crosslinking agent including
three or more carboxyl groups may be poly(acrylic acid-maleic
acid).
[0189] Accordingly, the hydrophilic coating layer may be formed to
have a thickness in a range of 5 to 20%, and preferably, in a range
of 8 to 18% in comparison with an average diameter of the
nanofibers. As an example, the hydrophilic coating layer may be
formed to have a thickness of 12% in comparison with the average
diameter of the nanofibers. When the hydrophilic coating layer is
formed to have a thickness of less than 5% in comparison with the
average diameter of the nanofibers, since a target degree of the
adhesive property is not embodied such that the hydrophilic coating
layer and the positively charged coating layer are delaminated
during a backwashing process in which an excessive pressure is
applied, filtration efficiency with respect to contaminants such as
microbes, an anionic compound, viruses, and the like may not be
provided as a target degree. When the hydrophilic coating layer is
formed to have a thickness of more than 20%, it is not easy to
decrease a weight of the filter medium. Also, as a size and
porosity of pores are reduced, water permeability of the solution
to be filtered may be degraded.
[0190] Next, description on a fiber-forming component which forms
the nanofiber webs 111 and 112 and an average diameter of the
nanofibers are equal to those of the first embodiment of the
present invention and as such will be omitted.
[0191] Also, an average pore diameter of the nanofiber webs 111 and
112 may be 0.1 to 3 .mu.m, preferably, in a range of 0.15 to 2
.mu.m, and for example, may be 0.25 .mu.m. When the average
diameter of the nanofiber webs 111 and 112 is less than 0.1 .mu.m,
water permeability with respect to a solution to be filtered may be
degraded. When the average diameter exceeds 3 .mu.m, filtration
efficiency with respect to contaminants such as microbes, an
anionic compound, viruses, and the like may not be high.
[0192] Also, porosity of the nanofiber webs 111 and 112 may be 40
to 90%, and preferably, in a range of 45 to 80%. For example, the
porosity of the nanofiber webs 111 and 112 may be 45%. When the
porosity of the nanofiber webs 111 and 112 is less than 40%, water
permeability with respect to a solution to be filtered may be
degraded. When the porosity exceeds 90%, filtration efficiency of
the filter medium with respect to contaminants such as microbes, an
anionic compound, viruses, and the like may not be high.
[0193] Also, description on other components included in the filter
medium 1000 are equal to those of the first embodiment of the
present invention and as such will be omitted.
[0194] Meanwhile, the filter medium 1000 according to the third
embodiment of the present invention may be manufactured through
operations including (1) forming a fiber web using nanofibers
formed by electrospinning a spinning solution, (2) manufacturing a
nanofiber web by including a positively charged coating layer
including a positively charged compound on at least a part of an
outer surface of the nanofibers, (3) laminating the nanofiber web
with a second support, and (4) disposing and laminating the
nanofiber web and the second support, which are laminated, on each
of both sides of a first support such that the second support comes
into contact with the first support.
[0195] First, (1) the forming of the fiber web using nanofibers
formed by electrospinning the spinning solution will be
described.
[0196] The fiber web may be formed using any method of forming a
three-dimensional network-shaped fiber web using nanofibers without
limitation. Preferably, the fiber web may be formed by
electrospinning a spinning solution including a fluorine-based
compound onto the second support.
[0197] The spinning solution may include, for example, a
fluorine-based compound and a solvent as the fiber-forming
component. 5 to 30 wt %, and preferably, 8 to 20 wt % of the
fluorine-based compound may be included in the spinning solution.
As an example, 15 wt % of the fluorine-based compound may be
included in the spinning solution. When the fluorine-based compound
is less than 5 wt %, it is difficult to form fibers. When being
spun, the fluorine-based compound is not spun in a fiber shape and
is sprayed in a droplet state to form a film shape. Otherwise, even
when spinning is performed, many beads are formed and the solvent
is not well volatilized such that a phenomenon in which pores are
blocked during a calendering process which will be described may
occur. Also, when the fluorine-based compound exceeds 30 wt %,
viscosity increases and solidification occurs on a surface of the
solution such that it is difficult to perform spinning for a long
time, and a diameter of fibers increases such that it is impossible
to form a fiber shape having a size of submicrometer.
[0198] As the solvent, any solvents may be used without limitation
that do not generate precipitations while dissolving the
fluorine-based compound which is a fiber-forming component and do
not influence spinning properties of nanofibers, which will be
described below. Preferably, any one or more selected from the
group consisting of r-butyrolactone, cyclohexanone, 3-hexanone,
3-heptanone, 3-octanone, N-methylpyrrolidone, dimethylacetamide,
acetone dimethyl sulfoxide, and dimethylformamide may be included.
As an example, the solvent may be a mixed solvent of
dimethylacetamide and acetone.
[0199] Meanwhile, description on electrospinning conditions and the
like are equal to those of the above-described first embodiment and
as such will be omitted.
[0200] Next, (2) the manufacturing of the nanofiber web by
including the positively charged coating layer including the
positively charged compound on at least the part of the outer
surface of the nanofibers will be described.
[0201] Accordingly to one embodiment, the operation (2) may include
(2-1) preparing a positively charged coating composition including
a solvent, a positively charged compound, and a binder and (2-2)
manufacturing the nanofiber web including the positively charged
coating layer by treating the fiber web with the positively charged
coating composition.
[0202] In the operation (2-1), the solvent included in the
positively charged coating composition may include one or more
types of solvents selected from the group consisting of purified
water, ethanol, methanol, ethylene glycol, acetic acid, hexene,
cyclohexene, cyclopentane, diisobutylene, 1-pentene, carbon
disulfide, carbon tetrachloride, 1-chlorobutene, 1-choloropentane,
o-xylene, diisopropyl ether, 2-chloropropane, toluene, diethyl
ether, diethyl sulfide, dichloromethane, 4-methyl-2-propanone,
tetrahydrofuran, 1,2-dichloroethane, 2-butanone, 1-nitropropane,
acetone, 1,4-dioxane, ethyl acetate, methyl acetate, 1-pentanol,
dimethyl sulfoxide, aniline, nitromethane, acetonitrile, pyridine,
2-butoxyethanol, 1-propanol, and 2-propanol, but is not limited
thereto, and a well-known solvent which does not influence mixing
and properties of the coating composition may be used.
[0203] 3 to 30 parts by weight, and preferably, 5 to 25 parts by
weight of the positively charged compound may be included with
respect to 100 parts by weight of the solvent. As an example, 15
parts by weight of the positively charged compound may be included
with respect to 100 parts by weight of the solvent. When the
positively charged compound is less than 3 parts by weight with
respect to 100 parts by weight of the solvent, a content of a
positively charged material covering the nanofibers is low such
that adsorption performance of the filter medium with respect to
contaminants having negative ions may be degraded. When the
positively charged compound exceeds 30 parts of weight, a content
of the positively charged compound is excessively high such that
mechanical properties of the nanofibers forming the positively
charged coating layer is degraded such that the nanofibers are
segmented or secede from the nanofiber web during backwashing and
filtration efficiency and water permeability are degraded.
[0204] Also, the binder increases an adhesive force of the
positively charged coating layer to prevent easy separation from
the surface of the nanofibers and may be included 1 to 5 parts by
weight, and preferably, 1.5 to 4.5 parts by weight with respect to
100 parts by weight of the solvent. As an example, the binder may
be included 3 parts by weight with respect to 100 parts by weight
of the solvent. When the binder is less than 1 part by weight with
respect to 100 parts by weight of the solvent, as the positively
charged coating layer is delaminated during a backwashing process
in which an excessive pressure is applied, durability against
backwashing is degraded such that filtration efficiency with
respect to contaminants such as microbes, cationic compounds,
viruses, and the like may not be provided as a target degree and
the positively charged compound may remain in filtrate. When 5
parts by weight is exceeded, a size and porosity of pores are
reduced such that water permeability of a solution to be filtered
may be degraded.
[0205] Afterwards, as the operation (2-2), an operation of forming
the positively charged coating layer by treating the nanofiber web
with the coating composition is performed.
[0206] As the coating method, any well-known coating method which
has no influence on properties of the nanofiber web having
nanofibers and fine porosity may be used without limitation, and
preferably, a dip coating process or a spray coating process may be
used.
[0207] When the dip coating process is used as an example of the
coating process, the nanofiber web, on which the positively charged
coating layer is formed, may be obtained by dipping and agitating
the nanofiber web to be coated in the coating composition at room
temperature under atmospheric conditions, removing an unreacted
material through filtration, cleaning the nanofiber web using
deionized (Di)-water, and drying the nanofiber web at room
temperature.
[0208] When the spray process is used as another example of the
coating process, it is possible to design a process in which a
coating composition suctioned in one direction is sprayed on and
covers the surface of the nanofiber web. Here, the coating
composition may be suctioned from separate lines in one line at the
same time and then mixed (in-line mixed) due to a difference in
pressures applied by spraying. Afterwards, the positively charged
coating layer may be formed by spraying the coating composition
onto a surface of a medium through a spray outlet.
[0209] Meanwhile, when the positively charged coating layer is
formed by treating the nanofiber web with the coating composition,
an operation of forming a hydrophilic coating layer may be further
included between the operations (1) and (2) in order to improve
adhesion between the nanofibers and the positively charged coating
layer.
[0210] The hydrophilic coating layer may be formed including a
hydrophilic polymer or may be formed by crosslinking a hydrophilic
polymer using a crosslinking agent. When the hydrophilic polymer is
formed by crosslinking using the crosslinking agent, the
crosslinking agent may be included in a range of 3 to 20 parts by
weight, and preferably, in a range of 8 to 15 parts by weight with
respect to 100 parts by weight of the hydrophilic polymer. As an
example, 15 parts by weight of the crosslinking agent may be
included with respect to 100 parts by weight of the hydrophilic
polymer. When the crosslinking agent is less than 3 parts by weight
with respect to 100 parts by weight of the hydrophilic polymer, a
target degree of an adhesive property between the nanofibers and
the positively charged coating layer may not be provided. When the
crosslinking agent is more than 20 parts by weight, porosity and a
mechanical property of the nanofibers are degraded such that the
nanofibers may be segmented or secede from the nanofiber web in
backwashing and filtration efficiency and water permeability may be
degraded.
[0211] Also, according to another embodiment of the present
invention, the operation (2) may be embodied using a method of
forming the positively charged coating layer by plating the
nanofibers with the positively charged compound to surround an
entirety of the outer surface of the nanofibers.
[0212] Although one of well-known positively charged compound
plating methods may be used in positively charged compound-plating,
in consideration of properties of the nanofibers, an electroless
plating method may be used. Hereinafter, a method of plating the
outer surface of the nanofibers forming the fiber web with the
positively charged compound using the electroless plating method
will be described as a reference.
[0213] The electroless plating method uses a substitution reaction.
In general, a method of plating a surface of a target material, in
which a material to be plated is dipped into a plating solution
including a reducible complexing material and is reduced to a
positively charged compound by adding a reductant thereto, is
used.
[0214] The plating solution may be a mixture solution including a
reducible solution, which is substituted for a positively charged
compound, and a positively charged compound providing solution
which provides a complexing material. As the reducible solution,
hydrazine (N.sub.2H.sub.4), lithium borohydride, sodium
borohydride, aluminum borohydride, sodium hypophosphite
(NaH.sub.2PO.sub.2), and the like, which are inorganic reductants,
and formaldehyde (HCHO), acetaldehyde (CH.sub.3CHO), benzaldehyde
(C.sub.6H.sub.5CHO), acrolein (CH.sub.2.dbd.CHCHO), glucose, and
the like, which are organic reductants, may be used. Among these,
glucose may be used. As a reductant aqueous solution, an aqueous
solution in which concentration of a reductant is 2 to 20% (w/v)
may be used.
[0215] Also, as the positively charged compound providing solution,
one of well-known positively charged compound providing solutions
may be used without limitation within a range which has no
influence on properties of the nanofibers.
[0216] The positively charged coating layer may be formed on the
surface of the nanofibers forming the nanofiber webs 111 and 112 by
dipping the nanofiber webs 111 and 112 into the above-described
plating solution. In consideration of a thickness of the positively
charged coating layer being plated and a surface area, the
nanofiber webs 111 and 112 may be dipped into the plating solution
for 1 to 10 hours. When dipping is performed for less than one
hour, the surface of the nanofibers may not be plated adequately
with the positively charged compound such that filtration
performance with respect to contaminants such as microbes, anionic
compounds, viruses, and the like may be degraded. Also, when
dipping is performed for more than ten hours, the surface of the
nanofibers is plated excessively with the positively charged
compound such that there may be a problem in decreasing a weight of
the filter medium and a size of pores decreases such that
penetration of a solution to be filtered may be degraded.
[0217] Here, in a case of using a method of applying the reductant
to the plating solution, since a reduction reaction occurs not only
on the surface of the material to be plated but also in the plating
solution, the surface of the nanofiber webs are soaked in the
reducible solution in a small quantity before being dipped into the
plating solution such that the positively charged compound is
obtained by reduction only on the surface of the nanofiber webs so
as to prevent an unnecessary reduction reaction.
[0218] Meanwhile, in the present invention, a pretreatment process
may be performed on the fiber web before the above-described
electroless plating in order to prevent filtration performance with
respect to contaminants such as microbes, anionic compounds,
viruses, and the like from being degraded after backwashing by the
plated positively charged coating layer being taken off in
backwashing due to excessive water pressure which is higher than
usual, to prevent pores of the filter medium from being blocked and
damaged by the taken-off positively charged compound, and/or to
further prevent contamination of the filtrate from being induced.
Here, the pretreatment process may be a catalyst-treatment
operation or a nanofiber etching operation.
[0219] The catalyst-treatment operation is a treatment process for
improving adhesion with a metal by initiating a chemical reaction
with the metal on a surface of a fiber which is a nonconductor
during electroless plating and may be an operation for forming an
electroless plating film without stains on a surface of nanofiber.
The etching operation may be a process for improving wettability of
nanofibers with respect to the plating solution and obtaining an
anchor effect.
[0220] Also, according to another embodiment of the present
invention, the operation (2) may be embodied using a method of
forming the positively charged coating layer on a part of the outer
surface of the nanofibers by vapor-depositing the positively
charged compound on the nanofibers exposed at one surface of the
fiber web.
[0221] A method of vapor-depositing the positively charged compound
may be any one selected from the group consisting of sputtering,
ion plating, arc deposition, ion beam assisted deposition, and
resistance heating vacuum evaporation. For example, as the method
of vapor-depositing the positively charged compound, a resistance
heating vacuum evaporation method may be used.
[0222] In a resistance heating vacuum evaporation system, a
positively charged compound vapor-depositing material, which is
heated in a vacuum chamber and vaporized into a gas phase, may be
provided at a top of a hot plate and a substrate holder may be
disposed at a part facing the positively charged compound
vapor-depositing material at a distance.
[0223] In the present invention, the fiber web, on which the
positively charged compound vapor-depositing material will be
vapor-deposited, is wound on a first bobbin disposed outside one
side of the vacuum chamber and the fiber web passes through a
bottom of the substrate holder at a certain speed while being
guided by a guide roller in the vacuum chamber such that vapor
deposition may be performed on the surface of the fiber web
according to evaporation of the positively charged compound
vapor-depositing material. Afterwards, the nanofiber webs 111 and
112, on which the positively charged coating layer is formed, are
withdrawn to the other side of the vacuum chamber and are wound on
a second bobbin such that positively charged compound
vapor-deposition may be consecutively performed.
[0224] Meanwhile, the present invention may further include forming
a primer layer capable of maximizing adhesion between the
positively charged coating layer and the fiber web by performing
surface treatment on the fiber web before the forming of the
positively charged coating layer through vapor deposition to
prevent filtration performance with respect to contaminants such as
microbes, anionic compounds, viruses, and the like after
backwashing from being degraded by the positively charged coating
layer being removed due to excessive water pressure which is higher
than usual in backwashing, to prevent pores of the filter medium
from being blocked and damaged by removed metal particles, and/or
to further prevent contamination of the filtrate from being
induced.
[0225] The primer layer may be formed through a process in which a
nonvolatile primer material having polarity is applied and dried at
a uniform thickness, in which methyl methacrylate, polyether
modified dimethylpolysiloxane copolymer, methyl ethyl ketone, vinyl
chloride-vinyl acetate copolymer, toluene, and the like may be
used.
[0226] Also, instead of the surface treatment of the primer layer,
an operation of performing plasma-treatment using a plasma
generator installed in the vacuum chamber before vapor deposition
may be further included. When the plasma treatment is performed on
the fiber web, the surface of the fiber web is activated such that
a polar functional group (OH- and H+) with respect to a metal
material to be vapor-deposited is assigned and cleaned and fine
prominences and depressions are formed so as to increase adhesion
between the fiber web and the positively charged coating layer. As
a reaction gas used in the plasma treatment, any one of
fluorocarbon (CF4), argon (Ar), zenon (Ze), helium (He), nitrogen
(N2), oxygen (O2), and a mixture thereof may be used.
[0227] Next, (3) the laminating of the nanofiber webs with the
second support will be described.
[0228] When the second support is provided using low melting point
composite fibers, bonding between the nanofiber web and the second
support through heat fusion may be performed at the same time
through the calendering process.
[0229] Also, an additional hot-melt powder or hot-melt web may be
further interposed to bind the second support to the nanofiber web.
Here, a temperature of applied heat may be 60 to 190.degree. C. and
an applied pressure may be 0.1 to 10 kgf/cm.sup.2 but the
temperature and pressure are not limited thereto. However,
components such as the hot-melt powder, which is separately added
for binding, generate fumes or are melted in a process of
laminating supports or laminating a support with nanofibers and
block pores frequently such that it is impossible to achieve a flow
rate of the filter medium which is initially designed. Also, since
the components are soluble in a water treatment process such that
environmentally adverse problems may be caused, the second support
and the nanofiber web may be bound to each other without the
components.
[0230] Next, (4) the disposing and laminating of the nanofiber webs
and the second support, which are laminated, on each of both sides
of the first support such that the second support comes into
contact with the first support will be described.
[0231] In the operation (4), the first support and the second
support may be melted by applying one or more of heat and pressure
and laminated in order to dispose and laminate the nanofiber web
and the second support, which are laminated, on each of both sides
of the first support. Here, a specific method of applying heat
and/or pressure may be selected from well-known methods. As a
non-limiting example, a conventional calendering process may be
used in which a temperature of applied heat may be 70 to
190.degree. C. Also, when the calendering process is performed, the
process may be divided into several operations and be performed a
plurality of times. For example, secondary calendering may be
performed after primary calendering. Here, degree(s) of heat and/or
pressure, which are/is applied in the calendering processes, may be
equal or different. The bonding between the second support and the
first support through heat fusion may be performed through fusion
of the first support and the second support such that an additional
adhesive or an adhesive layer may be omitted.
[0232] Also, a filter medium 1000 according to a fourth embodiment
of the present invention includes, as shown in FIG. 1, a porous
first support 130, nanofiber webs 111 and 112 disposed above and
below the first support 130 and having a three-dimensional network
structure formed by laminating nanofibers including silver
nanoparticles and having a plurality of pores, and porous second
supports 121 and 122 interposed between the first support 130 and
the nanofiber webs 111 and 112, respectively.
[0233] Silver nanoparticles are included outside and/or inside the
nanofibers which form the nanofiber webs. As a manufacturing method
which will be described, the silver nanoparticles provided on the
nanofibers are spun on a spinning solution, while silver metallic
salt is included, to be included in the nanofibers so as to be more
advantageous to preventing separation of the silver nanoparticles
in comparison to a case of providing silver nanoparticles on a
surface of the manufactured nanofibers through an additional
process.
[0234] A filter medium formed of only conventional nanofibers may
effectively remove fine dust but does not have a means to sterilize
microbes, such as bacteria and the like, collected with the fine
dust. According to the present invention, since the nanofiber webs
111 and 112 are configured to include silver nanoparticles such
that silver nanoparticles are evenly distributed on the surface of
the nanofibers, even when an amount of silver which is relatively
smaller is used, an excellent antibacterial effect may be provided
and problems such as the above-described separation of silver
nanoparticles and the like may be solved.
[0235] However, to prevent the nanofibers forming the nanofiber
webs 111 and 112 from being broken and to maintain strength at a
certain degree or higher, an average particle diameter of the
nanoparticles included in the nanofiber webs 111 and 112 should be
taken into consideration. Accordingly, the average particle
diameter of the silver nanoparticles may be 10 to 500 nm. When the
average particle diameter of the silver nanoparticles is less than
10 nm, sterilizing ability and antibacterial ability are degraded
such that a function of an antibacterial filter may not be
performed. When the average particle diameter of the silver
nanoparticles exceeds 500 nm, an area of the silver nanoparticles
in comparison to a fiber-forming component of the nanofibers
increases such that mechanical strength of the nanofibers is
degraded, which is disadvantageous in terms of an aspect of
durability such as causing the nanofibers to be broken and the
like.
[0236] Also, since an antibacterial force of the silver
nanoparticles is a phenomenon which occurs at an interface between
the silver nanoparticles and contaminants, it is necessary that the
silver nanoparticles have a certain degree or more of a specific
surface area. The specific surface area of the fin silver
nanoparticles may be measured through nitrogen vapor adsorption.
The specific surface area may be designed in adequate consideration
of a desirable filter medium, a desirable silver nanoparticle
content, a desirable composition of a solution to be filtered, and
the like.
[0237] Next, description on a fiber-forming component which forms
the nanofiber webs 111 and 112, an average pore diameter, porosity,
and an average diameter of the nanofibers are equal to those of the
first embodiment of the present invention and as such will be
omitted.
[0238] Also, description on other components included in the filter
medium 1000 are equal to those of the first embodiment of the
present invention and as such will be omitted.
[0239] Meanwhile, the filter medium 1000 according to the fourth
embodiment of the present invention may be manufactured through
operations including (1) laminating nanofiber webs including silver
nanoparticles with a second support and (2) disposing and
laminating the nanofiber webs and the second support, which are
laminated, on both sides of a first support such that the second
support comes into contact with the first support.
[0240] First, as the operation (1) according to the present
invention, an operation of laminating the nanofiber webs including
silver nanoparticles with the second support is performed.
[0241] The nanofiber web may be formed using any method of forming
a three-dimensional network-shaped fiber web using nanofibers
without limitation. The nanofiber web may be formed by
electrospinning a spinning solution, in which metallic salts are
dissolved, onto the second support.
[0242] The spinning solution may include silver salts, a
fiber-forming component, and a solvent. As an example of the
fiber-forming component, a fluorine-based compound may be included.
5 to 30 wt %, and preferably, 8 to 20 wt % of the fluorine-based
compound may be included in the spinning solution. When the
fluorine-based compound is less than 5 wt %, it is difficult to
form fibers. When being spun, the fluorine-based compound is not
spun in a fiber shape and is sprayed in a droplet state to form a
film shape. Otherwise, even when spinning is performed, many beads
are formed and the solvent is not well volatilized such that a
phenomenon in which pores are blocked during a calendering process
which will be described may occur. Also, when the fluorine-based
compound exceeds 30 wt %, viscosity increases and solidification
occurs on a surface of the solution such that it is difficult to
perform spinning for a long time, and a diameter of fibers
increases such that it is impossible to form a fiber shape having a
size of submicrometer.
[0243] The silver salts are a source for providing Ag positive ions
and may be one or more types of the silver salts selected from the
group consisting of silver nitrate, silver sulfate, silver
chloride, and the like. 1 to 20 wt %, and preferably, 5 to 15 wt %
of the silver salts may be included. When the silver salts are less
than 1 wt %, an antibacterial ability of the silver nanoparticles
decreases such that reduction into silver nanoparticles may be
difficult. Also, when the silver salts exceed 20 wt %, strength of
the nanofibers is degraded such that durability of the filter
medium may be degraded. Also, silver ions are precipitated such
that a change in color may be caused in which a color thereof
changes to brown after drying.
[0244] As the solvent, any solvents may be used without limitation
that do not generate precipitations while dissolving the silver
salts and the fluorine-based compound which is a fiber-forming
component and do not influence spinning properties of nanofibers
and a diameter of fibers, which will be described below.
Preferably, any one or more selected from the group consisting of
cyclohexanone, 3-hexanone, 3-heptanone, 3-octanone,
N-methylpyrrolidone, dimethylacetamide, acetone dimethyl sulfoxide,
and dimethylformamide may be included. As an example, the solvent
may be a mixed solvent of dimethylacetamide and acetone.
[0245] Meanwhile, description on electrospinning conditions and the
like are equal to those of the above-described first embodiment and
as such will be omitted.
[0246] Silver nanoparticles may be reduced on a surface of the
manufactured nanofiber web using one of methods such as emission of
ultraviolet (UV) rays or gamma rays, ultrasonic treatment, addition
of a reductant, thermal treatment, and the like. In comparison to a
method of electrospinning premanufactured silver nanoparticles in a
polymer solution, through the above method, an advantage is
provided in which small and even silver nanoparticles may be formed
in the nanofibers.
[0247] Also, the nanofiber web may be formed directly on the second
support by electrospinning the nanofibers directly on the
above-described second support. The nanofibers
accumulated/collected on the second support have a
three-dimensional network structure and may be embodied as the
nanofiber web having a three-dimensional network structure by
further applying heat and/or pressure to the accumulated/collected
nanofibers to retain porosity, an pore diameter, and a basis weight
adequate for realizing desirable water permeability and filtration
efficiency of a separation membrane. A specific method of applying
heat and/or pressure may be selected from well-known methods. As a
non-limiting example, a conventional calendering process may be
used in which a temperature of applied heat may be 70 to
190.degree. C. Also, when the calendering process is performed, the
process may be divided into several operations and performed a
plurality of times. For example, a drying process for removing a
part or an entirety of a solvent and water remaining on the
nanofibers is performed through primary calendering and then
secondary calendering may be performed to adjust pores and to
improve strength. Here, degree(s) of heat and/or pressure, which
are/is applied in the calendering processes, may be equal or
different.
[0248] When the second support is provided using low melting point
composite fibers, bonding between the nanofiber web and the second
support through heat fusion may be performed at the same time
through the calendering process.
[0249] Also, an additional hot-melt powder or hot-melt web may be
further interposed to bind the second support to the nanofiber web.
Here, a temperature of applied heat may be 60 to 190.degree. C. and
an applied pressure may be 0.1 to 10 kgf/cm.sup.2 but the
temperature and pressure are not limited thereto. However,
components such as the hot-melt powder, which is separately added
for binding, generate fumes or are melted in a process of
laminating supports or laminating a support with nanofibers and
block pores frequently such that it is impossible to achieve a flow
rate of the filter medium which is initially designed. Also, since
the components are soluble in a water treatment process such that
environmentally adverse problems may be caused, the second support
and the nanofiber web may be bound to each other without the
components.
[0250] Next, before the operation (2) which will be described
below, an operation of forming a hydrophilic coating layer by
treating the nanofiber web with a hydrophilic coating layer-forming
composition may be performed.
[0251] However, since the hydrophilic coating layer may be formed
on the silver nanoparticles formed on the surface of the
nanofibers, coating may be performed within process conditions and
a range of having no influence on properties of the silver
nanoparticles such as a unique antibacterial property, adhesion,
and the like.
[0252] In detail, the operation may be performed including treating
the nanofiber web with the hydrophilic coating layer-forming
composition and forming the hydrophilic coating layer by thermally
treating the hydrophilic coating layer-forming composition.
[0253] First, the hydrophilic coating layer-forming composition may
include a hydrophilic component and a crosslinking component, and
for example, include polyvinyl alcohol, a crosslinking agent
including a carboxyl group, and a solvent dissolving the same, for
example, water. The hydrophilic coating layer-forming composition
may include 2 to 20 parts by weight of the crosslinking agent and
1,000 to 100,000 parts by weight of the solvent with respect to 100
parts by weight of polyvinyl alcohol.
[0254] Meanwhile, when the nanofibers forming the manufactured
nanofiber web include a fluorine-based compound, due to strong
hydrophobicity, a coating layer may not be formed on the surface
adequately even when being treated using the above-described
hydrophilic coating layer-forming composition. Accordingly, the
hydrophilic coating layer-forming composition may further include a
wettability enhancer to well be wetted in the outer surface of the
nanofibers with the hydrophilic coating layer-forming
composition.
[0255] As the wettability enhancer, any one of components which can
improve wettability of the outer surface of the hydrophobic
nanofibers with respect to a hydrophilic solution and are soluble
in the hydrophilic coating layer-forming composition may be used
without limitation. As an example, the wettability enhancer may be
one or more components selected from the group consisting of
isopropyl alcohol, ethyl alcohol, and methyl alcohol. Also, the
wettability enhancer may be included in a range of 1,000 to 100,000
parts by weight with respect to 100 parts by weight of polyvinyl
alcohol included in the hydrophilic coating layer-forming
composition. When the wettability enhancer is provided at less than
1,000 parts by weight, wettability of the nanofibers is improved
insignificantly such that the hydrophilic coating layer may not be
easily formed and the hydrophilic coating layer may be frequently
delaminated. Also, when the wettability enhancer is provided at
more than 100,000 parts by weight, the wettability may be
insignificantly improved and concentrations of polyvinyl alcohol
and the crosslinking agent included in the hydrophilic coating
layer-forming composition are decreased such that the hydrophilic
coating layer may not be easily formed.
[0256] Meanwhile, the hydrophilic coating layer may be formed by
pretreating the nanofiber web with the wettability enhancer and
then treating the nanofiber web with the hydrophilic coating
layer-forming composition while the hydrophilic coating
layer-forming composition does not include the wettability
enhancer. However, when the nanofiber web is dipped into the
hydrophilic coating layer-forming composition while the wettability
enhancer is held by pores, the wettability enhancer held by the
pores is discharged from the nanofiber web, and at the same time,
time consumed when the hydrophilic coating layer-forming
composition penetrates the pores increases such that manufacturing
time increases. Also, since a degree of penetration of the
hydrophilic coating layer-forming composition varies according to a
thickness of the nanofiber web and a diameter of the pores, the
hydrophilic coating layer may be non-uniformly formed for each
position of the fiber web. In addition, as the hydrophilic coating
layer is non-uniformly formed, the pores at a part of the nanofiber
web are blocked by the hydrophilic coating layer. In this case,
since an initially designed pore structure of the nanofiber web
changes, a desirable flow rate may not be obtained. Accordingly,
the hydrophilic coating layer-forming composition, which includes
the wettability enhancer, is advantageous in reducing a
manufacturing time, simplifying a manufacturing process, and
improving formability of the hydrophilic coating layer at the same
time without change in a pore structure of the nanofiber web.
[0257] As a method of forming the above-described hydrophilic
coating layer-forming composition on the nanofiber web, any one of
well-known coating methods may be employed without limitation. For
example, dipping, spraying methods, and the like may be used.
[0258] Afterwards, an operation of forming the hydrophilic coating
layer by thermally treating the hydrophilic coating layer-forming
composition on the nanofiber web may be performed. Through the
thermal treatment, a process of drying the solvent among the
hydrophilic coating layer-forming composition may be performed at
the same time. The thermal treatment may be performed by a dryer.
Here, a temperature of applied heat may be 80 to 160.degree. C. and
a treatment time may be 1 to 60 minutes, but the temperature and
treatment time are not limited thereto.
[0259] Next, as the operation (2) according to the present
invention, an operation of disposing and laminating the nanofiber
webs and the second support, which are laminated, on both sides of
the first support such that the second support, which are laminated
with the nanofiber webs, comes into contact with the first support
is performed.
[0260] The operation (2) may be performed through operations
including (2-1) laminating the second support and the nanofiber
webs which are laminated in the operation (1) on both sides of the
first support and (2-2) fusing the first support and the second
support by applying any one or more of heat and pressure.
[0261] In the operation (2-2), a specific method of applying heat
and/or pressure may be selected from well-known methods. As a
non-limiting example, a conventional calendering process may be
used in which a temperature of applied heat may be 70 to
190.degree. C. Also, when the calendering process is performed, the
process may be divided into several operations and be performed a
plurality of times. For example, secondary calendering may be
performed after primary calendering. Here, degree(s) of heat and/or
pressure, which are/is applied in the calendering processes, may be
equal or different. Bonding between the second support and the
first support through heat fusion may be performed through the
operation (2-2) such that an additional adhesive or an adhesive
layer may be omitted.
[0262] Meanwhile, the present invention provides a flat filter unit
which includes a filter medium manufactured using the
above-described manufacturing method.
[0263] As shown in FIG. 5A, the filter medium 1000 may be embodied
as a flat filter unit 2000. In detail, the flat filter unit 2000
includes the filter medium 1000 and a support frame 1100 which
includes a flow path for discharging a filtrate filtered by the
filter medium 1000 to the outside and supports an edge of the
filter medium 1000.
[0264] Also, an inlet port 1110 which forms a pressure difference
(grain) between the outside and the inside of the filter medium
1000 may be provided in any one area of the support frame 1100.
Also, a flow path, through which the filtrate filtered by the
nanofiber webs passes through a support in which the second support
and the first support are laminated in the filter medium 1000 and
is discharged to the outside, may be formed in the support frame
1100.
[0265] In more detail, in the filter unit 2000 as shown in FIG. 5A,
when a suction force at high pressure is applied through the inlet
port 1110, a solution P which is to be filtered, which is disposed
outside the filter medium 1000, may move toward the inside of the
filter medium 1000, a filtrate Q1 filtered through nanofiber webs
101 and 102, may flow along a flow path formed through a support
200, in which the second support and the first support are
laminated, and may flow into a flow path E provided outside the
support frame 1100, and an inflow filtrate Q2 may be discharged to
the outside through the inlet port 1110.
[0266] Also, the flat filter unit 2000 as shown in FIG. 5A may
embody a filter module in which a plurality of such flat filter
units are spaced at certain intervals apart in one external case.
Also, a plurality of such filter modules may be laminated/blocked
to form a large water treatment apparatus.
[0267] In the filter medium according to the present invention,
deformation and damage to a shape and a structure of the filter
medium may be minimized and a flow path may be easily secured so as
to have a high flow rate in a water treatment operation. Also,
despite high pressure applied in backwashing, an extending use
period is provided due to excellent durability of the filter
medium, excellent water permeability and chemical resistance are
provided by uniformly coating a surface thereof with hydrophilic
components, contamination is easily controlled, and filtration
performance with respect to contaminants having positive ions such
as a cationic compound and the like is excellent such that the
filter medium is variously applicable to a variety of water
treatment fields.
MODES OF THE INVENTION
[0268] Although the following embodiments of the present invention
will be described in more detail, the following embodiments do not
limit the scope of the present invention and should be construed as
aiding in understanding of the present invention.
Example 1
[0269] (1) Manufacturing of Hydrophilic Coating Composition
[0270] As a first solvent, a mixture solution was prepared by
dissolving 10 g of polyvinyl alcohol (Kuraray Co., Ltd, PVA217)
having 1,800 degrees of polymerization and 88% degrees of
saponification as a hydrophilic polymer compound in 500 g of
ultrapure water at a temperature of 80.degree. C. for six hours
using a magnetic bar, and a first solution was prepared by cooling
the mixture solution at room temperature, mixing with 1.5 g of
sulfosuccinic acid (Aldrich, SSA) as a first crosslinking agent,
and dissolving at room temperature for twelve hours.
[0271] As a second solvent, a second solution was prepared by
dissolving 10 g of poly(styrene sulfonic acid-co-maleic acid) in
500 g of ultrapure water as a second crosslinking agent at room
temperature for six hours using a magnetic bar. Afterwards, a
coating solution was prepared by mixing and dissolving the first
solution and the second solution for twelve hours. Afterwards, a
hydrophilic coating composition was manufactured by adding and
mixing 500 g of isopropyl alcohol (Duksan Scientific Corp, IPA), as
a wettability enhancer, in the coating solution, like a weight
ratio of the ultrapure water, for two hours.
[0272] (2) Manufacturing of Filter Medium
[0273] To prepare a spinning solution, a mixture solution was
prepared by dissolving 12 g of polyvinylidene fluoride (Arkema Co.,
Ltd, Kynar761), as a fiber-forming component, in 88 g of a mixed
solvent, in which dimethylacetamide and acetone are mixed at a
weight ratio of 70:30, at a temperature of 80.degree. C. for six
hours using a magnetic bar. The spinning solution was injected into
a solution tank of an electrospinning device and was discharged at
a speed of 15 .mu.l/min/hole. Here, in a spinning section, a
temperature of 30.degree. C., a humidity of 50%, and 20 cm of a
distance between a collector and a spinning nozzle tip were
maintained. Afterwards, a fiber web formed of PVDF nanofibers was
manufactured by applying a voltage of 40 kV or higher to a spinning
nozzle pack using a high voltage generator simultaneously while
applying an air pressure of 0.03 MPa per a nozzle of the spinning
nozzle pack. Also, a laminate was manufactured by disposing
non-woven fabric (NamYang Nonwoven Fabric Co., Ltd, CCP40) formed
of low melting point composite fiber having an average thickness of
200 .mu.m and a melting point of 120.degree. C. and including a
sheath portion formed of polyethylene and a core portion of
polypropylene, as a second support, on one surface of the nanofiber
web, and then laminating the second support with the nanofiber web
by performing a calendering process by applying heat and pressure
of a temperature of 140.degree. C. and 1 kgf/cm.sup.2.
[0274] Afterwards, the manufactured lamination was impregnated with
the manufactured hydrophilic coating composition through a dipping
process and then dried in a dryer at a temperature of 100.degree.
C. for five minutes. A curing reaction was performed with drying
such that a hydrophilic coating layer was formed on the
lamination.
[0275] Also, the hydrophilic coating layer formed on the second
support was removed through cleaning using 5 L of pure water, and
two pieces of the lamination, from which the hydrophilic coating
layer formed on the second support is removed, were disposed on
both sides of a first support such that the second support comes
into contact with the first support. Here, as the first support,
non-woven fabric (NamYang Nonwoven Fabric Co., Ltd, NP450) formed
of low melting point composite fiber having an average thickness of
5 mm and a melting point of about 120.degree. C. and including a
sheath portion of polyethylene and a core portion of polypropylene
was used. Afterwards, a filter medium was manufactured by applying
heat at a temperature of 140.degree. C. and a pressure of 1
kgf/cm.sup.2.
Examples 2 to 18 and Comparative Examples 1 to 3
[0276] Filter media were manufactured by performing the same as in
Example 1 while a degree of polymerization and a degree of
saponification of a hydrophilic polymer compound and a crosslinking
agent content, a weight rate between crosslinking agents, a
wettability enhancer content, and the like were changed as shown in
following Tables 1 to 4.
Experimental Example
[0277] Each of filter media manufactured according to examples and
comparative examples was embodied as a filter unit as shown in FIG.
5A, and the following properties were evaluated and shown in Tables
1 to 4.
[0278] 1. Measurement of Relative Water Permeability
[0279] With respect to filter units embodied using the filter media
manufactured according to the examples and comparative examples,
water permeability per 0.5 m.sup.2 of an area of a specimen was
measured by applying a driving pressure of 50 kPa, and then water
permeability of each of filter media according to other examples
and comparative examples was measured on the basis of water
permeability of the filter medium of Example 1 as 100 as a
reference.
[0280] 2. Evaluation of Filtration Efficiency of Positive Ions
[0281] With respect to the filter units embodied using filter media
manufactured according to the examples and comparative examples,
filtration efficiency with respect to Na+ was measured through ion
chromatography analysis.
[0282] 3. Evaluation of Durability Against Backwashing
[0283] With respect to the filter units embodied using the filter
media manufactured according to the examples and comparative
examples, backwashing was performed under conditions in which the
filter unit was immersed into water and then water (400 LMH) was
pressurized for two minutes per 0.5 m.sup.2 of an area of a
specimen by applying a driving pressure of 50 kPa. Then, durability
against backwashing was evaluated. A case in which no abnormalities
occur is O and a case in which any problems such as delamination of
a silver antibacterial layer, delamination between layers, and the
like occur is X.
[0284] 4. Evaluation of Filtration Efficiency of Positive Ions
after Backwashing
[0285] With respect to the filter units embodied using filter media
manufactured according to the examples and comparative examples,
after performing the backwashing, filtration efficiency with
respect to Na+ was measured through ion chromatography
analysis.
TABLE-US-00001 TABLE 1 Classification Example 1 Example 2 Example 3
Example 4 Example 5 Example 6 Hydrophilic PVA Degree of 1800 300
1500 2500 1800 1800 coating polymerization composition Degree of 88
88 88 88 83 86 saponification (%) Crosslinking Content (part(s) 115
115 115 115 115 115 agent by weight) Weight ratio between 1:6.7
1:6.7 1:6.7 1:6.7 1:6.7 1:6.7 first and second crosslinking agents
Wettability Content (part(s) 5000 5000 5000 5000 5000 5000 enhancer
by weight) Whether first support is included .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. Whether second support is included .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. Relative water permeability (%) 100 105 102 74 104
101 Positive ion filtration efficiency (%) 95 86 94 97 84 94
Durability against backwashing .largecircle. X .largecircle.
.largecircle. X .largecircle. Positive ion filtration efficiency
(%) 95 69 94 96 66 94
TABLE-US-00002 TABLE 2 Classification Example 7 Example 8 Example 9
Example 10 Example 11 Example 12 Hydrophilic PVA Degree of 1800
1800 1800 1800 1800 1800 coating polymerization composition Degree
of 89 92 88 88 88 88 saponification (%) Crosslinking Content
(part(s) 115 115 70 90 140 160 agent by weight) Weight ratio
between 1:6.7 1:6.7 1:6.7 1:6.7 1:6.7 1:6.7 first and second
crosslinking agents Wettability Content (part(s) 5000 5000 5000
5000 5000 5000 enhancer by weight) Whether first support is
included .largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. Whether second support is included
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. Relative water permeability (%) 99 --
107 103 91 72 Positive ion filtration efficiency (%) 96 -- 87 93 96
97 Durability against backwashing .largecircle. -- X .largecircle.
.largecircle. .largecircle. Positive ion filtration efficiency (%)
after backwashing 96 -- 63 93 96 97
TABLE-US-00003 TABLE 3 Classification Example 13 Example 14 Example
15 Example 16 Example 17 Example 18 Hydrophilic PVA Degree of 1800
1800 1800 1800 1800 1800 coating polymerization composition Degree
of 88 88 88 88 88 88 saponification (%) Crosslinking Content
(part(s) 115 115 115 115 115 115 agent by weight) Weight ratio
between 1:1 1:5 1:8 1:12 1:6.7 1:6.7 first and second crosslinking
agents Wettability Content (part(s) 5000 5000 5000 5000 500 25000
enhancer by weight) Whether first support is included .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. Whether second support is included .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. Relative water permeability (%) 86 92 83 75 73 83
Positive ion filtration efficiency (%) 84 91 96 98 93 78 Durability
against backwashing .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. X Positive ion filtration efficiency
(%) after backwashing 84 91 96 98 93 61
TABLE-US-00004 TABLE 4 Comparative Comparative Comparative
Classification Example 1 Example 2 Example 3 Hydrophilic PVA Degree
of -- 1800 1800 coating polymerization composition Degree of -- 88
88 saponification (%) Crosslinking Content (part(s) -- 115 115
agent by weight) Weight ratio between -- 1:6.7 1:6.7 first and
second crosslinking agents Wettability Content (part(s) -- 5000
5000 enhancer by weight) Whether first support is included
.largecircle. .largecircle. X Whether second support is included
.largecircle. X .largecircle. Relative water permeability (%) 22
118 112 Positive ion filtration efficiency (%) 11 86 83 Durability
against backwashing .largecircle. X X Positive ion filtration
efficiency (%) after backwashing 10 51 39
[0286] As seen in Tables 1 to 4, Examples 1, 3, 6, 7, 10, 11, 14,
and 15, which satisfied all of a degree of polymerization and a
degree of saponification of a hydrophilic polymer compound, a
crosslinking agent content, a weight ratio between crosslinking
agents, a wettability enhancer content, and the like according to
the present invention, were excellent in water permeability,
filtration efficiency, durability against backwashing, filtration
efficiency after the backwashing in comparison to Examples 2, 4, 5,
8, 9, 12, 13, 16 to 18 and comparative Examples 1 to 3, in which
even any one among such factors was omitted.
[0287] Meanwhile, since a degree of saponification is excessive
such that a coating layer is not formed in Example 8, it is
impossible to measure properties thereof
Example 19
[0288] First, to prepare a spinning solution, a mixture solution
was prepared by dissolving 12 g of polyvinylidene fluoride (Arkema
Co., Ltd, Kynar761), as a fiber-forming component, in 88 g of a
mixed solvent, in which dimethylacetamide and acetone were mixed at
a weight ratio of 70:30, at a temperature of 80.degree. C. for six
hours using a magnetic bar. The spinning solution was injected into
a solution tank of an electrospinning device and was discharged at
a speed of 15 .mu.l/min/hole. Here, in a spinning section, a
temperature of 30.degree. C., a humidity of 50%, and 20 cm of a
distance between a collector and a spinning nozzle tip were
maintained. Afterwards, a fiber web formed of PVDF nanofibers was
manufactured by applying a voltage of 40 kV or higher to a spinning
nozzle pack using a high voltage generator simultaneously while
applying an air pressure of 0.03 MPa per a nozzle of the spinning
nozzle pack. Also, to form a hydrophilic coating layer on an outer
surface of nanofibers, a first mixture solution was prepared by
dissolving 7143 parts by weight of pure water, as a solvent, with
respect to 100 parts by weight of polyvinyl alcohol (Kuraray Co.,
Ltd, PVA217), as a hydrophilic polymer, at a temperature of
80.degree. C. for six hours using a magnetic bar. A second mixture
solution was prepared by lowering a temperature of the first
mixture solution to room temperature and then mixing and dissolving
15 parts by weight of poly(acrylic acid-maleic acid) (Aldrich,
PAM), with respect to 100 parts by weight of the hydrophilic
polymer, with the first mixture solution at room temperature for
twelve hours. Also, a hydrophilic coating solution was prepared by
adding and mixing 7143 parts by weight of isopropyl alcohol (Duksan
Scientific Corp, IPA), with respect to 100 parts by weight of the
hydrophilic polymer, with the second solution for two hours.
Afterwards, a hydrophilic coating layer was formed on an outer
surface of nanofibers by dipping a fiber web into the manufactured
hydrophilic coating solution and drying the same at a temperature
of 110.degree. C. for five minutes.
[0289] Also, a nanofiber web, which has 0.8 .mu.m of an average
pore diameter and a porosity of 70%, was manufactured by cleaning
the fiber web, forming a primer layer by applying and drying
toluene to the cleaned fiber web, and forming a silver
antibacterial layer having an average thickness of 50 nm by
vapor-depositing silver through a resistance heating vacuum
evaporation. Here, a weight of the silver antibacterial layer
provided on the nanofiber web is 60% in comparison to a weight of
an entirety of the nanofibers. Afterwards, non-woven fabric
(NamYang Nonwoven Fabric Co., Ltd, CCP40) formed of low melting
point composite fiber having an average thickness of 200 .mu.m and
a melting point of 120.degree. C. and including a sheath portion
formed of polyethylene and a core portion of polypropylene, was
disposed, as a second support, on one surface of the nanofiber web,
and then the second support and the nanofiber web were laminated by
performing a calendering process by applying heat and pressure of a
temperature of 140.degree. C. and 1 kgf/cm.sup.2.
[0290] Also, two lamination products formed by laminating the
second support and the nanofiber web were disposed on both sides of
the first support to allow the second supports to come into contact
with the first support. Here, as the first support, non-woven
fabric (NamYang Nonwoven Fabric Co., Ltd, NP450) formed of low
melting point composite fiber having an average thickness of 5 mm
and a melting point of about 120.degree. C. and including a sheath
portion of polyethylene and a core portion of polypropylene was
used. Afterwards, a filter medium was manufactured by applying heat
at a temperature of 140.degree. C. and a pressure of 1
kgf/cm.sup.2.
Example 20
[0291] A filter medium was manufactured in the same manner as in
Example 19 except that a fiber web formed of PVDF nanofibers was
manufactured, cleaning and forming a primer layer was changed to
etching of nanofibers, and vapor-deposition was changed to
electroless plating performed by dipping the manufactured fiber web
into a silver plating solution including hydrazine and silver
nitrate for five hours.
Examples 21 to 26 and Comparative Examples 4 to 6
[0292] Filter media shown in following Tables 5 and 6 were
manufactured in the same manner as in Example 19 while a thickness
of a silver antibacterial layer, a weight of the silver
antibacterial layer with respect to a weight of nanofibers, an
average pore diameter and porosity of a nanofiber web, a first
support, a second support, and whether the silver antibacterial
layer was included were changed as shown in Tables 5 and 6.
Experimental Example 2
[0293] Each of filter media manufactured according to examples and
comparative examples was embodied as a filter unit as shown in FIG.
4A, and the following properties were evaluated and shown in Tables
5 and 6.
[0294] 1. Measurement of Relative Water Permeability
[0295] With respect to filter units embodied using the filter media
manufactured according to the examples and comparative examples,
water permeability per 0.5 m.sup.2 of an area of a specimen was
measured by applying a driving pressure of 50 kPa, and then water
permeability of each of filter media according to other examples
and comparative examples was measured on the basis of water
permeability of the filter medium of Example 19 as 100 as a
reference.
[0296] 2. Measurement of Antibacterial Property
[0297] With respect to filter units embodied using filter media
manufactured according to examples and comparative examples,
antibacterial properties were manufactured on the basis of KS K
0693: 2011, and bacteriostatic reduction rates with respect to
Staphylococcus aureus (ATCC 6538) and Klebsiella pneumoniae (ATCC
4352), as publicly announced used strains, were measured.
[0298] 3. Evaluation of Durability Against Backwashing
[0299] With respect to the filter units embodied using the filter
media manufactured according to the examples and comparative
examples, backwashing was performed under conditions in which the
filter unit was immersed into water and then water (400 LMH) was
pressurized for two minutes per 0.5 m.sup.2 of an area of a
specimen by applying a driving pressure of 50 kPa. Then, durability
against backwashing was evaluated. A case in which no abnormalities
occur is O and a case in which any problems such as delamination of
a silver antibacterial layer, delamination between layers, and the
like occur is X.
[0300] 4. Measurement of Antibacterial Property after
Backwashing
[0301] With respect to filter units embodied using filter media
manufactured according to examples and comparative examples,
antibacterial properties were manufactured, after performing the
backwashing, on the basis of KS K 0693: 2011, and bacteriostatic
reduction rates with respect to Staphylococcus aureus (ATCC 6538)
and Klebsiella pneumoniae (ATCC 4352), as publicly announced used
strains, were measured after the backwashing.
TABLE-US-00005 TABLE 5 Classification Example 19 Example 20 Example
21 Example 22 Example 23 Example 24 Method of forming silver Vapor
Plating Plating Plating Plating Plating antibacterial layer forming
method deposition Thickness of silver 50 50 2 10 100 150
antibacterial layer (nm) Weight of silver antibacterial 60 133 12
88 189 276 layer in comparison to weight of nanofibers (%) Average
pore diameter of 0.8 0.75 1.5 1.1 0.53 0.28 nanofiber web (.mu.m)
Porosity of nanofiber web (%) 70 67 82 77 58 53 Whether first
support is included .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. Whether second support is
included .largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. Relative water permeability (%) 100 98
133 105 82 54 Bacteriostatic Staphylococcus 99.9 99.9 99.9 99.9
99.9 99.9 reduction rate (%) (antibacterial Pneumonia 99.9 99.9
99.9 99.9 99.9 99.9 property) bacilli (%) Durability against
backwashing .largecircle. .largecircle. X .largecircle.
.largecircle. .largecircle. Bacteriostatic Staphylococcus 99.9 99.9
78.2 97.7 99.9 99.9 reduction rate (%) (antibacterial Pneumonia
99.9 99.9 81.7 98.2 99.9 99.9 property) after bacilli (%)
backwashing
TABLE-US-00006 TABLE 6 Comparative Comparative Comparative
Classification Example 25 Example 26 Example 4 Example 5 Example 6
Method of forming silver Vapor Plating -- Plating Plating
antibacterial layer forming method deposition Thickness of silver 5
280 -- 50 50 antibacterial layer (nm) Weight of silver
antibacterial 10 550 -- 30 30 layer in comparison to weight of
nanofibers (%) Average pore diameter of 1.5 0.12 1 1 1 nanofiber
web (.mu.m) Porosity of nanofiber web (%) 85 43 70 70 70 Whether
first support is included .largecircle. .largecircle. .largecircle.
.largecircle. X Whether second support is included .largecircle.
.largecircle. .largecircle. X .largecircle. Relative water
permeability (%) 141 37 100 117 110 Bacteriostatic Staphylococcus
99.9 99.9 0 99.9 99.9 reduction rate (%) (antibacterial Pneumonia
99.9 99.9 0 99.9 99.9 property) bacilli (%) Durability against
backwashing X .largecircle. .largecircle. X X Bacteriostatic
Staphylococcus 86.7 99.9 0 72 54.2 reduction rate (%)
(antibacterial Pneumonia 85.1 99.9 0 67.9 48.8 property) after
bacilli (%) backwashing
[0302] As shown in Tables 5 and 6, Examples 19, 20, 22, and 23,
which satisfied a thickness of a silver antibacterial layer, a
weight of the silver antibacterial layer in comparison to a weight
of nanofibers, an average pore diameter and porosity of a nanofiber
web, a first support, a second support, and whether the silver
antibacterial layer was included, and the like according to the
present invention, were excellent in all of water permeability, a
bacteriostatic reduction rate (antibacterial property), durability
against backwashing, and a bacteriostatic reduction rate
(antibacterial property) after backwashing in comparison to
Examples 21, 24, 25, and 26 and Comparative Examples 4 to 6 in
which even any one among such factors was omitted.
Example 27
[0303] First, to prepare a spinning solution, a mixture solution
was prepared by dissolving 12 g of polyvinylidene fluoride (Arkema
Co., Ltd, Kynar761), as a fiber-forming component, in 88 g of a
mixed solvent, in which dimethylacetamide and acetone were mixed at
a weight ratio of 70:30, at a temperature of 80.degree. C. for six
hours using a magnetic bar. The spinning solution was injected into
a solution tank of an electrospinning device and was discharged at
a speed of 15 .mu.l/min/hole. Here, in a spinning section, a
temperature of 30.degree. C., a humidity of 50%, and 20 cm of a
distance between a collector and a spinning nozzle tip were
maintained. Afterwards, a fiber web formed of PVDF nanofibers
having an average diameter of 250 nm was manufactured by applying a
voltage of 40 kV or higher to a spinning nozzle pack using a high
voltage generator simultaneously while applying an air pressure of
0.03 MPa per a nozzle of the spinning nozzle pack.
[0304] Also, to form a hydrophilic coating layer on an outer
surface of nanofibers, a first mixture solution was prepared by
dissolving 7143 parts by weight of pure water, as a solvent, with
respect to 100 parts by weight of polyvinyl alcohol (Kuraray Co.,
Ltd, PVA217), as a hydrophilic polymer, at a temperature of
80.degree. C. for six hours using a magnetic bar. A second mixture
solution was prepared by lowering a temperature of the first
mixture solution to room temperature and then mixing and dissolving
15 parts by weight of poly(acrylic acid-maleic acid) (Aldrich,
PAM), with respect to 100 parts by weight of the hydrophilic
polymer, with the first mixture solution at room temperature for
twelve hours. Also, a hydrophilic coating solution was prepared by
adding and mixing 7143 parts by weight of isopropyl alcohol (Duksan
Scientific Corp, IPA), with respect to 100 parts by weight of the
hydrophilic polymer, with the second solution for two hours.
Afterwards, a hydrophilic coating layer was formed on an outer
surface of nanofibers by dipping a fiber web into the manufactured
hydrophilic coating solution and drying the same at a temperature
of 110.degree. C. for five minutes. Here, an average thickness of
the hydrophilic coating layer was 30 nm.
[0305] Afterwards, to form a positively charged coating layer on
the fiber web on which the hydrophilic coating layer is formed, a
positively charged coating solution was prepared by mixing 100
parts by weight of pure water as a solvent with 0.5 part by weight
of polyethylene imide as a positively charged compound, and with
0.1 parts by weight of polyvinyl alcohol and poly(acrylic
acid-maleic acid) at a weight ratio of 10:1 as a binder. A
nanofiber web, on which the positively charged coating layer is
formed and which has an average pore diameter of 0.3 .mu.m and a
porosity of 45%, was manufactured by dipping the fiber web, on
which the hydrophilic coating layer is formed, into the positively
charged coating solution and drying the dipped fiber web at a
temperature 110.degree. C. for 10 minutes. Here, an average
thickness of the positively charged coating layer was 30 nm.
Afterwards, non-woven fabric (NamYang Nonwoven Fabric Co., Ltd,
CCP40) formed of low melting point composite fiber having an
average thickness of 200 .mu.m and a melting point of 120.degree.
C. and including a sheath portion formed of polyethylene and a core
portion of polypropylene, was disposed, as a second support, on one
surface of the nanofiber web, and then the second support and the
nanofiber web were laminated by performing a calendering process by
applying heat and pressure of a temperature of 140.degree. C. and 1
kgf/cm.sup.2.
[0306] Also, two lamination products formed by laminating the
second support and the nanofiber web were disposed on both sides of
the first support to allow the second supports to come into contact
with the first support. Here, as the first support, non-woven
fabric (NamYang Nonwoven Fabric Co., Ltd, NP450) formed of low
melting point composite fiber having an average thickness of 5 mm
and a melting point of about 120.degree. C. and including a sheath
portion of polyethylene and a core portion of polypropylene was
used. Afterwards, a filter medium was manufactured by applying heat
at a temperature of 140.degree. C. and a pressure of 1
kgf/cm.sup.2.
Example 28
[0307] First, to prepare a spinning solution, a mixture solution
was prepared by dissolving 12 g of polyvinylidene fluoride (Arkema
Co., Ltd, Kynar761), as a fiber-forming component, in 88 g of a
mixed solvent, in which dimethylacetamide and acetone were mixed at
a weight ratio of 70:30, at a temperature of 80.degree. C. for six
hours using a magnetic bar. The spinning solution was injected into
a solution tank of an electrospinning device and was discharged at
a speed of 15 .mu.l/min/hole. Here, in a spinning section, a
temperature of 30.degree. C., a humidity of 50%, and 20 cm of a
distance between a collector and a spinning nozzle tip were
maintained. Afterwards, a fiber web formed of polyvinylidene
fluoride (PVDF) nanofibers was manufactured by applying a voltage
of 40 kV or higher to a spinning nozzle pack using a high voltage
generator simultaneously while applying an air pressure of 0.03 MPa
per a nozzle of the spinning nozzle pack. Also, a nanofiber web,
which has 0.3 .mu.m of an average pore diameter and a porosity of
45%, was manufactured by cleaning the fiber web, forming a primer
layer by applying and drying toluene to the cleaned fiber web, and
forming a positively charged coating layer having an average
thickness of 50 nm by vapor-depositing silver through a resistance
heating vacuum evaporation. Here, a weight of the silver
antibacterial layer provided on the nanofiber web is 30% in
comparison to a weight of an entirety of the nanofibers.
Afterwards, non-woven fabric (NamYang Nonwoven Fabric Co., Ltd,
CCP40) formed of low melting point composite fiber having an
average thickness of 200 .mu.m and a melting point of 120.degree.
C. and including a sheath portion formed of polyethylene and a core
portion of polypropylene, was disposed, as a second support, on one
surface of the nanofiber web, and then the second support and the
nanofiber web were laminated by performing a calendering process by
applying heat and pressure of a temperature of 140.degree. C. and 1
kgf/cm.sup.2.
[0308] Also, two lamination products formed by laminating the
second support and the nanofiber web were disposed on both sides of
the first support to allow the second supports to come into contact
with the first support. Here, as the first support, non-woven
fabric (NamYang Nonwoven Fabric Co., Ltd, NP450) formed of low
melting point composite fiber having an average thickness of 5 mm
and a melting point of about 120.degree. C. and including a sheath
portion of polyethylene and a core portion of polypropylene was
used. Afterwards, a filter medium was manufactured by applying heat
at a temperature of 140.degree. C. and a pressure of 1
kgf/cm.sup.2.
Example 29
[0309] A filter medium was manufactured in the same manner as in
Example 28 except that a fiber web formed of PVDF nanofibers was
manufactured, cleaning and forming a primer layer was changed to
etching of nanofibers, vapor-deposition was changed to electroless
plating performed by dipping the manufactured fiber web into a
silver plating solution including hydrazine and silver nitrate for
five hours.
Examples 30 to 41 and Comparative Examples 7 to 9
[0310] Filter media shown in the following Tables 7 to 9 were
manufactured in the same manner as in Example 27 while a thickness
of a positively charged coating layer, a weight ratio between a
positively charged compound and a binder, a thickness of a
hydrophilic coating layer, an average pore diameter and porosity of
a nanofiber web, a first support, a second support, and whether the
positively charged coating layer was included were changed as shown
in Tables 7 to 9.
Experimental Example 3
[0311] Each of filter media manufactured according to examples and
comparative examples was embodied as in the filter unit as shown in
FIG. 5A, and the following properties were evaluated and shown in
Tables 7 to 9.
[0312] 1. Measurement of Relative Water Permeability
[0313] With respect to filter units embodied using the filter media
manufactured according to the examples and comparative examples,
water permeability per 0.5 m.sup.2 of an area of a specimen was
measured by applying a driving pressure of 50 kPa, and then water
permeability of each of filter media according to other examples
and comparative examples was measured on the basis of water
permeability of the filter medium of Example 27 as 100 as a
reference.
[0314] 2. Measurement of Zeta Potential
[0315] With respect to filter units embodied using filter media
manufactured according to examples and comparative examples, zeta
potential, on the basis of a pH of 7, was measured using a zeta
potential measurer (SurPASS 3, Anton Paar) capable of measuring a
zeta potential of a surface.
[0316] 3. Evaluation of Filtration Efficiency of Negative Ions
[0317] With respect to the filter units embodied using filter media
manufactured according to the examples and comparative examples,
filtration efficiency with respect to negative ions (Cl-) was
measured through ion chromatography analysis.
[0318] 4. Evaluation of Durability Against Backwashing
[0319] With respect to the filter units embodied using the filter
media manufactured according to the examples and comparative
examples, backwashing was performed under conditions in which the
filter unit was immersed into